Why Johnny can't clone: Common pitfalls and not so common solutions

The immune system of prokaryotes: potential applications and implications for gene editing

Gene therapy has revolutionized the treatment of genetic diseases. Spearheading this revolution are sophisticated genome editing methods such as TALENs, ZFNs, and CRISPR-Cas, which trace their origins back to prokaryotic immune systems. Prokaryotes have developed various antiviral defense systems to combat viral attacks and the invasion of genetic elements. The comprehension of these defense mechanisms has paved the way for the development of indispensable tools in molecular biology. Among them, restriction endonuclease originates from the innate immune system of bacteria. The CRISPR-Cas system, a widely applied genome editing technology, is derived from the prokaryotic adaptive immune system. Single-base editing is a precise editing tool based on CRISPR-Cas system that involves deamination of target base. It is worth noting that prokaryotes possess deamination enzymes as part of their defense arsenal over foreign genetic material. Furthermore, prokaryotic Argonauts (pAgo) proteins, also function in anti-phage defense, play an important role in complementing the CRISPR-Cas system by addressing certain limitations it may have. Recent studies have also shed light on the significance of Retron, a reverse transcription transposon previously showed potential in genome editing, has also come to light in the realm of prokaryotic immunity. These noteworthy findings highlight the importance of studying prokaryotic immune system for advancing genome editing techniques. Here, both the origin of prokaryotic immunity underlying aforementioned genome editing tools, and potential applications of deaminase, pAgo protein and reverse transcriptase in genome editing among prokaryotes were introduced, thus emphasizing the fundamental mechanism and significance of prokaryotic immunity.

Sustainable Methodologies for Efficient Gel Electrophoresis and Streamlined Screening of Difficult Plasmids

We describe a workflow for efficient, environmentally attentive, and sustainable practices related to routine agarose gel electrophoresis. The methods reduce plastic waste and improve efficiency, especially for the exhaustive screening of difficult-to-obtain plasmids. Sustainability is increased when agarose is used ten times over by virtue of a thorough recycling regimen. The workflow optimizes workspaces and standardizes lab practices for handling potentially hazardous waste, minimizing environmental harm. Safety, efficiency, and sustainability improve laboratory productivity, help minimize environmental contamination, and increase cost-effectiveness.

Golden Gate assembly of BioBrick-compliant parts using Type II restriction endonucleases

Aims: New methods of DNA recombination that capture the principal advantages of the BioBrick standard (ease of design) and Golden Gate assembly (decreased labor) are demonstrated here. Methods & materials: Both methods employ DNA methyltransferase expression vectors, available from Addgene, that protect selected sites on different plasmids from particular Type II restriction endonucleases. No other reagents are required. Results: The 4R/2M discontinuous DNA assembly is more efficient (produces more desired recombinant plasmids) and as specific (produces few undesired recombination products) as conventional subcloning. The 5RM continuous DNA assembly is approximately as efficient and specific as conventional Golden Gate assembly, even though in vivo methylation of one plasmid is incomplete. Conclusion: Both methylase-assisted methods streamline BioBrick assembly workflows without complicating the design of synthetic parts.

Preselector.uni-jena.de: optimize your cloning-a resource for identifying restriction enzymes for preselection reactions

Preselection digests are a common strategy to reduce the background in the ligation step of molecular cloning. However, choosing fitting restriction enzymes by hand is not trivial and may lead to errors, potentially costing a lot of time and work. We therefore created preselector.uni-jena.de (https://preselector.uni-jena.de/), a free online tool to find such restriction enzymes. The tool uses regular expressions to find recognition sites of restriction enzymes in the DNA sequences provided by the user. This new tool compares the sets of restriction sites and reports the enzymes that cut one sequence but not the other sequences to the user. These enzymes are then the ones suitable for a preselection digest. Thus, preselector.uni-jena.de is a fast, reliable, and free-to-use tool to help researchers designing preselection digestion strategies for their cloning.

Methylase-assisted subcloning for high throughput BioBrick assembly

The BioBrick standard makes possible iterated pairwise assembly of cloned parts without any depletion of unique restriction sites. Every part that conforms to the standard is compatible with every other part, thereby fostering a worldwide user community. The assembly methods, however, are labor intensive or inefficient compared to some newer ones so the standard may be falling out of favor. An easier way to assemble BioBricks is described herein. Plasmids encoding BioBrick parts are purified from Escherichia coli cells that express a foreign site-specific DNA methyltransferase, so that each is subsequently protected in vitro from the activity of a particular restriction endonuclease. Each plasmid is double-digested and all resulting restriction fragments are ligated together without gel purification. The ligation products are subsequently double-digested with another pair of restriction endonucleases so only the desired insert-recipient vector construct retains the capacity to transform E. coli. This 4R/2M BioBrick assembly protocol is more efficient and accurate than established workflows including 3A assembly. It is also much easier than gel purification to miniaturize, automate and perform more assembly reactions in parallel. As such, it should streamline DNA assembly for the existing community of BioBrick users, and possibly encourage others to join.

Homologous alignment cloning: a rapid, flexible and highly efficient general molecular cloning method

Homologous alignment cloning (HAC) is a rapid method of molecular cloning that facilitates low-cost, highly efficient cloning of polymerase chain reaction products into any plasmid vector in approximately 2 min. HAC facilitates insert integration due to a sequence alignment strategy, by way of short, vector-specific homology tails appended to insert during amplification. Simultaneous exposure of single-stranded fragment ends, utilising the 3′→5′ exonuclease activity of T4 DNA polymerase, creates overlapping homologous DNA on each molecule. The exonuclease activity of T4 polymerase is quenched simply by the addition of EDTA and a simple annealing step ensures high yield and high fidelity vector formation. The resultant recombinant plasmids are transformed into standard E. coli cloning strains and screened via established methods as necessary. HAC exploits reagents commonly found in molecular research laboratories and achieves efficiencies that exceed conventional cloning methods, including another ligation-independent method we tested. HAC is also suitable for combining multiple fragments in a single reaction, thus extending its flexibility.

Semi-automated Tip Snip cloning of restriction fragments into and out of plasmid polylinkers

Synthetic biologists rely on semi-synthetic recombinant plasmids, but DNA synthesis is constrained by practical limits on length, accuracy, and sequence composition. Cloned DNA parts can be assembled into longer constructs via subcloning, but conventional methods are labor-intensive. One-pot recombination reactions are more convenient but harder to troubleshoot, and those that depend on PCR to create fragments with compatible ends necessitate re-sequencing. The Tip Snip protocol described here enables the subcloning of an insert from one plasmid polylinker into another without PCR or gel purification steps. Cohesive ends of unwanted restriction fragments are snipped off by additional restriction endonucleases. The resulting short fragments (snippets) are eliminated by hybridization to complementary oligonucleotides (anti-snippets) and subsequent size-selection spin-column chromatography. Unwanted linear donor vectors are ligated to double-stranded oligonucleotides (unlinkers) so that only the desired insert and recipient plasmid form circular DNA capable of transforming bacteria. This new method is compatible with high-throughput processing and automated liquid handling, and because no specialized vectors, reagents, selection schemes, or analytical techniques are required, the barriers to adoption are low.