Name: plasmid-derived dna strand displacement gates for implementing chemical reaction networks
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Figures 1, 2, 3, 4, 6, 8 and Tables 2, 3, 10, 15, 16 are modified from Ref29. This work was supported by the National Science Foundation (grant NSF-CCF 1117143 and NSF-CCF 1162141 to G.S.). Y.-J. C. was supported by Taiwanese Government Fellowships. S.D.R was supported by the National Science Foundation Graduate Research Fellowship Program (GRFP).

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The authors declare no competing financial interests.

This paper describes a method for deriving ndsDNA gates from highly pure plasmid DNA. Moreover, a protocol is presented for characterizing gate performance using a fluorescence kinetics assay. Experimental data shows that the plasmid-derived system outperforms its synthetic counterpart even if the synthetic system is assembled from strands purified using polyacrylamide gel electrophoresis (PAGE). Likely, the improved performance of plasmid-derived gates is primarily due to the very high purity of the biological DNA. Synthetic DNA contains a variety of errors, in particular deletions that result in oligonucleotides of length n-1, and such side products are typically not completely removed in PAGE or high-performance liquid chromatography (HPLC) purification procedures. Similar improvements to the ones reported here were also observed in a previous study of a catalyzed hairpin amplifier that used DNA derived from biological sources21.
However, even the use of plasmid-derived gates cannot completely eliminate errors in the gate performance, for which there are at least two reasons: first over-digestion or lack of cut precision can lead to gates with too many nicks or nicks in the wrong positions. In either case, gates are more likely to participate in undesired reactions. Such problems may be eased by optimizing the amount of enzyme used (see Figure 4). Second, in these experiments, most inputs and auxiliary strands were synthetic DNA and thus contained deletions and mutations. In principle, all single-stranded input and auxiliary strands could also be obtained from phagemid DNA through a nicking enzyme digestion of the pre-encoded m13 viral genome26. Perhaps the circuit performance can be further improved using ssDNA derived from the bacterial genome.
While the use of plasmid-derived gates was found to improve circuit performance, an analysis of the cost and processing times revealed that while the production of plasmid-derived gates is slightly cheaper (Table 15), it takes 2-3 times longer processing time compared to assembly and purification of gates from commercially synthesized oligos (Table 16). The primary costs of plasmid-derived gates are gene synthesis and the use of restriction enzymes. For 300 pmole of gates (enough for 15 reactions at 30 nM), the estimated cost for Join gates is approximately $170 and $200 for Fork gates, the cost difference being due to the use of different nicking enzymes. In contrast, the chemical synthesis of the strands for the same gate costs around $260 including a PAGE purification fee. The primary time cost for plasmid-derived gates is in the cloning procedure, which, just like DNA synthesis, can be outsourced to a gene synthesis company. However, once assembled, plasmid-derived gates have the advantage that the host plasmids can easily be replicated and can be stored in the form of bacterial glycerol stocks. This makes it possible to reuse the gates many times over.
Looking forward, the improved performance of plasmid-derived gates could enable a much larger range of dynamics behaviors than have been experimentally demonstrated so far with DNA CRNs. For example, recent theoretical work47,48 suggested that self-organized spatial patterns at the macro-scale can be realized with DNA CRNs through a reaction diffusion mechanism. The method presented here provides a viable path for constructing the underlying molecular components for such self-patterning DNA materials. Though challenging, developing macro-scale morphologies in a programmable way would have significant implications in areas ranging from biomaterials research to regenerative medicine.

The predictability of Watson-Crick base pairing has allowed dynamic DNA nanotechnology to emerge as a programmable way to design molecular devices with dynamic properties1,2. In particular, DNA strand displacement &#8212; a programmable, competitive hybridization reaction &#8212; has proved to be a powerful mechanism for engineering dynamic DNA systems. In a DNA strand displacement reaction, an incoming oligonucleotide displaces a previously bound &#8220;output&#8221; strand from a complementary binding partner. Multiple such reactions can be chained together into multi-step reaction cascades with a high degree of control over the order and timing of individual reaction steps3. DNA strand displacement cascades have been used to create digital and analog molecular circuits4-7, switchable nanostructures8-10, autonomous molecular motors11-15, and non-covalent catalytic amplifiers13,16-21. Moreover, DNA devices using strand displacement reactions can be simulated and designed for diverse applications using computer-assisted design software22-24.
Currently, chemically synthesized DNA serves as the main material for DNA nanotechnology. However, errors in the DNA synthesis process, and the resulting imperfect oligonucleotides, are believed to limit performance of dynamic DNA devices by causing erroneous side reactions. For example, &#8220;leak&#8221; reactions can result in the release of an output oligonucleotide even in the absence of a reaction trigger. Such effects are most obvious in autocatalytic reaction cascades where even a minimal amount of initial leak will eventually result in the full activation of the cascade19,20. Conversely, reactions often fail to reach the expected level of activation because some components do not trigger even in the presence of the intended input7,25. To make the performance of DNA-based nanodevices comparable to their biological protein-based counterparts, such error modes need to be dramatically reduced.
Bacterial plasmids or other biological DNA could serve as a relatively cheap source of highly pure DNA for nanotechnology applications. Large amounts of DNA can be generated by replication in bacteria and the intrinsic proofreading abilities of living systems ensure the purity of the resulting DNA. In fact, several recent papers have recognized the potential utility of biological DNA for nanotechnology applications21,26-28. However, the fully double-stranded nature of plasmid DNA has so far prohibited its use as a material for making dynamic DNA devices, which typically consist of multiple oligonucleotides and contain both double-stranded and single-stranded domains. In a recent paper29 this issue was addressed and a new DNA gate architecture that consists primarily of nicked double-stranded DNA (ndsDNA) was introduced.
Importantly, systems of ndsDNA gates can be designed that realize the dynamics specified by any formal chemical reaction network (CRN)29. ndsDNA gates could thus be used, in principle, to create dynamical systems that exhibit oscillations and chaos, bistability and memory, Boolean logic or algorithmic behaviors30-38. For example, Ref. 29 demonstrated a three-reaction CRN that provided a molecular implementation of a &#8220;consensus&#8221; protocol, a type of distributed computing algorithm29,39,40. This work first demonstrated a novel use for the CRN formalism as a &#8220;programming language&#8221; for rapidly synthesizing functional molecular systems (Figure 1A).
Here, a detailed protocol for deriving ndsDNA gates from plasmid DNA is provided. First is a review of the sequence design process. Then follows an explanation of how synthetic oligonucleotides containing the gate sequences are cloned into plasmids and sequence verified and amplified via bacterial culture. Next, it is shown how ndsDNA gates can be derived from the plasmids by enzymatic processing (see Figure 2). Finally, a method for testing gate behavior using fluorescence kinetics assays is outlined.
Reaction mechanism 
As an example, the protocol focuses on the catalytic chemical reaction A+B-&#62;B+C. The species A, B, and C (&#8220;signals&#8221;, Figure 1B) all correspond to a different single-stranded DNA molecule. The sequences of these molecules are completely independent and the strands do not react with one another directly. The sequences of all signals have two different functional domains, i.e., subsequences that act together in strand displacement reactions: 1) a short toehold domain (labels ta, tb, tc) that is used for initiation of strand displacement reaction, and 2) a long domain (labels a, b, c) that determines the signal identity.
Interactions between signal strands are mediated by nicked double-stranded DNA (ndsDNA) gate complexes (called JoinAB and ForkBC) and auxiliary single-stranded species (&#60;tr r&#62;, &#60;b tr&#62;, &#60;c tb&#62; and &#60;i tc&#62;). The formal reaction A+B-&#62;B+C is executed through a series of strand displacement reaction steps, where each reaction step exposes a toehold for a subsequent reaction (Figure 1B). In this example, signals A and B are initially free in solution while signal C is bound to the fork gate. At the end of the reaction B and C are in solution. More generally, signals that are bound to a gate are inactive while signals that are free in solution are active, that is, they can participate in a strand displacement reaction as an input. The time course of the reaction is followed using a fluorescent reporter strategy (Figure 1C). In previous work29, it was demonstrated that this reaction mechanism not only realizes the correct stoichiometry but also the kinetics of the target reaction.

<table><tbody><tr><td>Phusion High-Fidelity PCR Master Mix with HF Buffer</td><td>NEB</td><td>M0531S</td><td></td></tr><tr><td>PvuII-HF</td><td>NEB</td><td>R3151L</td><td></td></tr><tr><td>PstI-HF</td><td>NEB</td><td>R3140S</td><td></td></tr><tr><td>Gibson Assembly Master Mix</td><td>NEB</td><td>E2611S</td><td></td></tr><tr><td>Terrific Broth, Modified</td><td>SIGMA-ALDRICH</td><td>T0918-250G</td><td></td></tr><tr><td>QIAprep Spin Miniprep Kit (250)</td><td>QIAGEN</td><td>27106</td><td></td></tr><tr><td>QIAGEN Hispeed Maxi-prep Kit</td><td>QIAGEN</td><td>12662</td><td></td></tr><tr><td>Nb.BsrDI</td><td>NEB</td><td>R0648L</td><td></td></tr><tr><td>Nt.BstNBI</td><td>NEB</td><td>R0607L</td><td></td></tr><tr><td>NanoDrop 2000c</td><td>Thermo Scientific</td><td></td><td></td></tr><tr><td>Double-stranded Genomic Blocks</td><td>IDT</td><td></td><td></td></tr><tr><td>Horiba Jobin-Yvon Spex Fluorolog-3 Fluorimeter</td><td>Horiba/Jobin Yvon</td><td></td><td></td></tr><tr><td>Synthetic Quartz Cells&amp;nbsp;</td><td>Starna</td><td>23-5.45-S0G-5</td><td></td></tr><tr><td>QIAGEN Gel Extraction Kit</td><td>QIAGEN</td><td>28706</td><td></td></tr><tr><td>Plasmid Backbones</td><td>BioBrick</td><td>E0240-pSB1A2</td><td>High copy number plasmid with Ampicillin resistance. Sequence can be found from http://parts.igem.org</td></tr></tbody></table>

plasmid-derived dna strand displacement gates for implementing chemical reaction networks

DNA nanotechnology requires large amounts of highly pure DNA as an engineering material. Plasmid DNA could meet this need since it is replicated with high fidelity, is readily amplified through bacterial culture and can be stored indefinitely in the form of bacterial glycerol stocks. However, the double-stranded nature of plasmid DNA has so far hindered its efficient use for construction of DNA nanostructures or devices that typically contain single-stranded or branched domains. In recent work, it was found that nicked double stranded DNA (ndsDNA) strand displacement gates could be sourced from plasmid DNA. The following is a protocol that details how these ndsDNA gates can be efficiently encoded in plasmids and can be derived from the plasmids through a small number of enzymatic processing steps. Also given is a protocol for testing ndsDNA gates using fluorescence kinetics measurements. NdsDNA gates can be used to implement arbitrary chemical reaction networks (CRNs) and thus provide a pathway towards the use of the CRN formalism as a prescriptive molecular programming language. To demonstrate this technology, a multi-step reaction cascade with catalytic kinetics is constructed. Further it is shown that plasmid-derived components perform better than identical components assembled from synthetic DNA.

Watch this Scientific Journal Video about Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks at JoVE.com

Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks

This protocol describes a method for deriving DNA strand displacement gates from plasmids and testing them using fluorescence kinetics measurements. Gates can be modularly composed into multi-component systems to approximate the behavior of formal chemical reaction networks (CRN), demonstrating a new use for CRNs as a molecular programming language.

DNA nanotechnology requires large amounts of highly pure DNA as an engineering material. Plasmid DNA could meet this need since it is replicated with high ...

plasmid-derived-dna-strand-displacement-gates-for-implementing

Nanyang Technological University

Research

JoVE Journal

Biology

14.3K Views.  University of Washington. This protocol describes a method for deriving DNA strand displacement gates from plasmids and testing them using fluorescence kinetics measurements. Gates can be modularly composed into multi-component systems to approximate the behavior of formal chemical reaction networks (CRN), demonstrating a new use for CRNs as a molecular programming language. 

Video: Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks

Designing a Bio-responsive Robot from DNA Origami

Nucleic acids are astonishingly versatile. In addition to their natural role as storage medium for biological information1, they can be utilized in parallel computing2,3 , recognize and bind molecular or cellular targets4,5 , catalyze chemical reactions6,7 , and generate calculated responses in a biological system8,9. Importantly, nucleic acids can be programmed to self-assemble into 2D and 3D structures10-12, enabling the integration of all these remarkable features in a single robot linking the sensing of biological cues to a preset response in order to exert a desired effect.
Creating shapes from nucleic acids was first proposed by Seeman13, and several variations on this theme have since been realized using various techniques11,12,14,15 . However, the most significant is perhaps the one proposed by Rothemund, termed scaffolded DNA origami16. In this technique, the folding of a long (&gt;7,000 bases) single-stranded DNA 'scaffold' is directed to a desired shape by hundreds of short complementary strands termed 'staples'. Folding is carried out by temperature annealing ramp. This technique was successfully demonstrated in the creation of a diverse array of 2D shapes with remarkable precision and robustness. DNA origami was later extended to 3D as well17,18 .
 
The current paper will focus on the caDNAno 2.0 software19 developed by Douglas and colleagues. caDNAno is a robust, user-friendly CAD tool enabling the design of 2D and 3D DNA origami shapes with versatile features. The design process relies on a systematic and accurate abstraction scheme for DNA structures, making it relatively straightforward and efficient.
In this paper we demonstrate the design of a DNA origami nanorobot that has been recently described20. This robot is 'robotic' in the sense that it links sensing to actuation, in order to perform a task. We explain how various sensing schemes can be integrated into the structure, and how this can be relayed to a desired effect. Finally we use Cando21 to simulate the mechanical properties of the designed shape. The concept we discuss can be adapted to multiple tasks and settings.

DNA origami is a powerful method for fabricating precise nanoscale objects by programming the self-assembly of DNA molecules. Here, we describe how DNA origami can be utilized to design a robotic robot capable of sensing biological cues and responding by shape shifting, subsequently relayed to a desired effect.

Nucleic acids are astonishingly versatile. In addition to their natural role as storage medium for biological information1, they can be utilized in ...

Bioengineering

Homemade Site Directed Mutagenesis of Whole Plasmids

Site directed mutagenesis of whole plasmids is a simple way to create slightly different variations of an original plasmid. With this method the cloned target gene can be altered by substitution, deletion or insertion of a few bases directly into a plasmid. It works by simply amplifying the whole plasmid, in a non PCR-based thermocycling reaction. During the reaction mutagenic primers, carrying the desired mutation, are integrated into the newly synthesized plasmid. In this video tutorial we demonstrate an easy and cost effective way to introduce base substitutions into a plasmid. The protocol works with standard reagents and is independent from commercial kits, which often are very expensive. Applying this protocol can reduce the total cost of a reaction to an eighth of what it costs using some of the commercial kits. In this video we also comment on critical steps during the process and give detailed instructions on how to design the mutagenic primers.

Site directed mutagenesis of whole plasmids is a simple way to create slightly different variations of an original plasmid. Here we demonstrate an easy and cost effective way to introduce base substitutions into a plasmid using standard reagents.

Site directed mutagenesis of whole plasmids is a simple way to create slightly different variations of an original plasmid. With this method the cloned ...

Automated Robotic Liquid Handling Assembly of Modular DNA Devices

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; represented by &#34;devices&#34; created as combinations of individual genetic components. However, manual assembly of such large numbers of devices is time-intensive, error-prone, and costly. The increasing sophistication and scale of synthetic biology research necessitates an efficient, reproducible way to accommodate large-scale, complex, and high throughput device construction.
Here, a DNA assembly protocol using the Type-IIS restriction endonuclease based Modular Cloning (MoClo) technique is automated on two liquid-handling robotic platforms. Automated liquid-handling robots require careful, often times tedious optimization of pipetting parameters for liquids of different viscosities (e.g. enzymes, DNA, water, buffers), as well as explicit programming to ensure correct aspiration and dispensing of DNA parts and reagents. This makes manual script writing for complex assemblies just as problematic as manual DNA assembly, and necessitates a software tool that can automate script generation. To this end, we have developed a web-based software tool, http://mocloassembly.com, for generating combinatorial DNA device libraries from basic DNA parts uploaded as Genbank files. We provide access to the tool, and an export file from our liquid handler software which includes optimized liquid classes, labware parameters, and deck layout. All DNA parts used are available through Addgene, and their digital maps can be accessed via the Boston University BDC ICE Registry. Together, these elements provide a foundation for other organizations to automate modular cloning experiments and similar protocols.
The automated DNA assembly workflow presented here enables the repeatable, automated, high-throughput production of DNA devices, and reduces the risk of human error arising from repetitive manual pipetting. Sequencing data show the automated DNA assembly reactions generated from this workflow are ~95% correct and require as little as 4% as much hands-on time, compared to manual reaction preparation.

Here, an automated workflow to perform modular DNA &#34;device&#34; assembly using a modular cloning DNA assembly method on liquid-handling robots is presented. The protocol uses an intuitive software tool for generating liquid handler picklists for combinatorial DNA device library generation, which we demonstrate using two liquid handling platforms.

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; ...

Using Synthetic Biology to Engineer Living Cells That Interface with Programmable Materials

We have developed an abiotic-biotic interface that allows engineered cells to control the material properties of a functionalized surface. This system is made by creating two modules: a synthetically engineered strain of E. coli cells and a functionalized material interface. Within this paper, we detail a protocol for genetically engineering selected behaviors within a strain of E. coli using molecular cloning strategies. Once developed, this strain produces elevated levels of biotin when exposed to a chemical inducer. Additionally, we detail protocols for creating two different functionalized surfaces, each of which is able to respond to cell-synthesized biotin. Taken together, we present a methodology for creating a linked, abiotic-biotic system that allows engineered cells to control material composition and assembly on nonliving substrates.

This paper presents a series of protocols for developing engineered cells and functionalized surfaces that enable synthetically engineered E. coli to control and manipulate programmable material surfaces.

We have developed an abiotic-biotic interface that allows engineered cells to control the material properties of a functionalized surface. This system is ...

Design and Synthesis of a Reconfigurable DNA Accordion Rack

DNA nanostructure-based mechanical systems or DNA nanomachines, which produce complex nanoscale motion in 2D and 3D in the nanometer to &#229;ngstr&#246;m resolution, show great potential in various fields of nanotechnology such as the molecular reactors, drug delivery, and nanoplasmonic systems. The reconfigurable DNA accordion rack, which can collectively manipulate a 2D or 3D nanoscale network of elements, in multiple stages in response to the DNA inputs, is described. The platform has potential to increase the number of elements that DNA nanomachines can control from a few elements to a network scale with multiple stages of reconfiguration.
In this protocol, we describe the entire experimental process of the reconfigurable DNA accordion rack of 6 by 6 meshes. The protocol includes a design rule and simulation procedure of the structures and a wet-lab experiment for synthesis and reconfiguration. In addition, analysis of the structure using TEM (transmission electron microscopy) and FRET (fluorescence resonance energy transfer) is included in the protocol. The novel design and simulation methods covered in this protocol will assist researchers to use the DNA accordion rack for further applications.

We describe the detailed protocol for design, simulation, wet-lab experiments, and analysis for a reconfigurable DNA accordion rack of 6 by 6 meshes.

DNA nanostructure-based mechanical systems or DNA nanomachines, which produce complex nanoscale motion in 2D and 3D in the nanometer to &#229;ngstr&#246;m ...

Functional Surface-immobilization of Genes Using Multistep Strand Displacement Lithography

Immobilization of genes on lithographically structured surfaces allows the study of compartmentalized gene expression processes in an open microfluidic bioreactor system. In contrast to other approaches towards artificial cellular systems, such a setup allows for a continuous supply with gene expression reagents and simultaneous draining of waste products. This facilitates the implementation of cell-free gene expression processes over extended periods of time, which is important for the realization of dynamic gene regulatory feedback systems. Here we provide a detailed protocol for the fabrication of genetic biochips using a simple-to-use lithographic technique based on DNA strand displacement reactions, which exclusively uses commercially available components. We also provide a protocol on the integration of compartmentalized genes with a polydimethylsiloxane (PDMS)-based microfluidic system. Furthermore, we show that the system is compatible with total internal reflection fluorescence (TIRF) microscopy, which can be used for the direct observation of molecular interactions between DNA and molecules contained in the expression mix.

We describe a simple lithographic procedure for the immobilization of gene-length DNA molecules on a surface, which can be used to perform cell-free gene expression experiments on biochips.

Immobilization of genes on lithographically structured surfaces allows the study of compartmentalized gene expression processes in an open microfluidic ...

Rapid Assembly of Multi-Gene Constructs using Modular Golden Gate Cloning

The Golden Gate cloning method enables the rapid assembly of multiple genes in any user-defined arrangement. It utilizes type IIS restriction enzymes that cut outside of their recognition sites and create a short overhang. This modular cloning (MoClo) system uses a hierarchical workflow in which different DNA parts, such as promoters, coding sequences (CDS), and terminators, are first cloned into an entry vector. Multiple entry vectors then assemble into transcription units. Several transcription units then connect into a multi-gene plasmid. The Golden Gate cloning strategy is of tremendous advantage because it allows scar-less, directional, and modular assembly in a one-pot reaction. The hierarchical workflow typically enables the facile cloning of a large variety of multi-gene constructs with no need for sequencing beyond entry vectors. The use of fluorescent protein dropouts enables easy visual screening. This work provides a detailed, step-by-step protocol for assembling multi-gene plasmids using the yeast modular cloning (MoClo) kit. We show optimal and suboptimal results of multi-gene plasmid assembly and provide a guide for screening for colonies. This cloning strategy is highly applicable for yeast metabolic engineering and other situations in which multi-gene plasmid cloning is required.

The goal of this protocol is to provide a detailed, step-by-step guide for assembling multi-gene constructs using the modular cloning system based on Golden Gate cloning. It also gives recommendations on critical steps to ensure optimal assembly based on our experiences.

The Golden Gate cloning method enables the rapid assembly of multiple genes in any user-defined arrangement. It utilizes type IIS restriction enzymes that ...

DNA-Tethered RNA Polymerase for Programmable In vitro Transcription and Molecular Computation

DNA nanotechnology enables programmable self-assembly of nucleic acids into user-prescribed shapes and dynamics for diverse applications. This work demonstrates that concepts from DNA nanotechnology can be used to program the enzymatic activity of the phage-derived T7 RNA polymerase (RNAP) and build scalable synthetic gene regulatory networks. First, an oligonucleotide-tethered T7 RNAP is engineered via expression of an N-terminally SNAP-tagged RNAP and subsequent chemical coupling of the SNAP-tag with a benzylguanine (BG)-modified oligonucleotide. Next, nucleic-acid strand displacement is used to program polymerase transcription on-demand. In addition, auxiliary nucleic acid assemblies can be used as &#34;artificial transcription factors&#34; to regulate the interactions between the DNA-programmed T7 RNAP with its DNA templates. This in vitro transcription regulatory mechanism can implement a variety of circuit behaviors such as digital logic, feedback, cascading, and multiplexing. The composability of this gene regulatory architecture facilitates design abstraction, standardization, and scaling. These features will enable the rapid prototyping of in vitro&#160;genetic devices for applications such as bio-sensing, disease detection, and data storage.

We describe the engineering of a novel DNA-tethered T7 RNA polymerase to regulate in vitro transcription reactions. We discuss the steps for protein synthesis and characterization, validate proof-of-concept transcriptional regulation, and discuss its applications in molecular computing, diagnostics, and molecular information processing.

DNA nanotechnology enables programmable self-assembly of nucleic acids into user-prescribed shapes and dynamics for diverse applications. This work ...

Gene Digital Circuits Based on CRISPR-Cas Systems and Anti-CRISPR Proteins

Synthetic gene Boolean gates and digital circuits have a broad range of applications, from medical diagnostics to environmental care. The discovery of the CRISPR-Cas systems and their natural inhibitors-the anti-CRISPR proteins (Acrs)-provides a new tool to design and implement in vivo gene digital circuits. Here, we describe a protocol that follows the idea of the "Design-Build-Test-Learn" biological engineering cycle and makes use of dCas9/dCas12a together with their corresponding Acrs to establish small transcriptional networks, some of which behave like Boolean gates, in Saccharomyces cerevisiae. These results point out the properties of dCas9/dCas12a as transcription factors. In particular, to achieve maximal activation of gene expression, dSpCas9 needs to interact with an engineered scaffold RNA that collects multiple copies of the VP64 activation domain (AD). In contrast, dCas12a shall be fused, at the C terminus, with the strong VP64-p65-Rta (VPR) AD. Furthermore, the activity of both Cas proteins is not enhanced by increasing the amount of sgRNA/crRNA in the cell. This article also explains how to build Boolean gates based on the CRISPR-dCas-Acr interaction. The AcrIIA4 fused hormone-binding domain of the human estrogen receptor is the core of a NOT gate responsive to &#946;-estradiol, whereas AcrVAs synthesized by the inducible GAL1 promoter permits to mimic both YES and NOT gates with galactose as an input. In the latter circuits, AcrVA5, together with dLbCas12a, showed the best logic behavior.

CRISPR-Cas systems and anti-CRISPR proteins were integrated into the scheme of Boolean gates in Saccharomyces cerevisiae. The new small logic circuits showed good performance and deepened the understanding of both dCas9/dCas12a-based transcription factors and the properties of anti-CRISPR proteins.

Synthetic gene Boolean gates and digital circuits have a broad range of applications, from medical diagnostics to environmental care. The discovery of the ...

Generation of Plasmid Vectors Expressing FLAG-tagged Proteins Under the Regulation of Human Elongation Factor-1&#945; Promoter Using Gibson Assembly

Gibson assembly (GA) cloning offers a rapid, reliable, and flexible alternative to conventional DNA cloning methods. We used GA to create customized plasmids for expression of exogenous genes in mouse embryonic stem cells (mESCs). Expression of exogenous genes under the control of the SV40 or human cytomegalovirus promoters diminishes quickly after transfection into mESCs. A remedy for this diminished expression is to use the human elongation factor-1 alpha (hEF1&#945;) promoter to drive gene expression. Plasmid vectors containing hEF1&#945; are not as widely available as SV40- or CMV-containing plasmids, especially those also containing N-terminal 3xFLAG-tags. The protocol described here is a rapid method to create plasmids expressing FLAG-tagged CstF-64 and CstF-64 mutant under the expressional regulation of the hEF1&#945; promoter. GA uses a blend of DNA exonuclease, DNA polymerase and DNA ligase to make cloning of overlapping ends of DNA fragments possible. Based on the template DNAs we had available, we designed our constructs to be assembled into a single sequence. Our design used four DNA fragments: pcDNA 3.1 vector backbone, hEF1&#945; promoter part 1, hEF1&#945; promoter part 2 (which contained 3xFLAG-tag purchased as a double-stranded synthetic DNA fragment), and either CstF-64 or specific CstF-64 mutant. The sequences of these fragments were uploaded to a primer generation tool to design appropriate PCR primers for generating the DNA fragments. After PCR, DNA fragments were mixed with the vector containing the selective marker and the GA cloning reaction was assembled. Plasmids from individual transformed bacterial colonies were isolated. Initial screen of the plasmids was done by restriction digestion, followed by sequencing. In conclusion, GA allowed us to create customized plasmids for gene expression in 5 days, including construct screens and verification.

Synthesis of custom plasmids is labor and time consuming. This protocol describes the use of Gibson assembly cloning to reduce the work and duration of custom DNA cloning procedure. The protocol described also produces reliable tagged protein constructs for mammalian expression at similar cost to the traditional cut-and-paste DNA cloning.

Gibson assembly (GA) cloning offers a rapid, reliable, and flexible alternative to conventional DNA cloning methods. We used GA to create customized ...