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Pushing the Limits of DNA Assembly

Posted by Guest Blogger on Sep 6, 2017 9:01:33 AM

This post was contributed by guest blogger Lydia Morrison from New England Biolabs.

What is DNA assembly? In the context of cloning, DNA assembly refers to a method of physically joining multiple fragments of DNA to create a synthetically designed DNA sequence. There are multiple methods of DNA assembly available, including: Gibson Assembly®, BioBrick® Assembly, Golden Gate Assembly, and NEBuilder® HiFi DNA Assembly. Gibson Assembly allows the production of scarless DNA constructs using homologous regions to guide the joining reaction. BioBrick Assembly will leave scar regions at the site of fragment joining, but this is fine for its goal of creating a choice of standardized constructs and tools for the rational and simple shuffling of DNA regions. Golden Gate Assembly also allows the creation of standardized DNA constructs, but its use of Type IIS restriction enzymes results in scarless assembly. Finally, the NEBuilder® HiFi DNA Assembly method from New England Biolabs® has minimal upfront requirements and allows you to expediently join multiple synthetic fragments, create multiple mutations in one or multiple fragments, and generate constructs for producing single-guide RNAs – but it also allows you to skip purification steps and end-repair steps with well-designed fragment overlap sections, while still creating scarless plasmid inserts. 

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Topics: Techniques, Plasmid Cloning

Plasmids for Endogenous Gene Tagging in Human Cells

Posted by Guest Blogger on Apr 6, 2017 9:02:59 AM

This post was contributed by the gene editing team at the Allen Institute for Cell Science. Learn more by visiting the Allen Cell Explorer at allencell.org and the Allen Institute website at alleninstitute.org.

A classic challenge in cell biology is making sure that what we observe through the microscope represents reality as accurately as possible. This is especially true in the case of protein tagging to elucidate cellular structures. Overexpression methods flood the cell with protein, which can both interfere with a cell’s normal function and result in a ubiquitous background signal that makes it hard to visualize the precise location of the protein or structure of interest.

Endogenous gene tagging is an ideal solution because it allows for tagging and visualization of specific, individual proteins under endogenous regulatory control. But even with the advent of CRISPR/Cas9 technology, inserting large tags into a precise location in the genome is still inefficient, particularly in human cell lines. Furthermore, the quality control necessary to ensure the edited cells are behaving normally can be prohibitively expensive for many labs.

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Topics: Plasmid How To, CRISPR, Techniques

Deep Mutational Scanning with One Pot Saturation Mutagenesis

Posted by Beth Kenkel on Feb 22, 2017 10:30:00 AM

Scientists use deep mutational scanning to simultaneously test how multiple amino acid changes affect a protein of interest’s function. This technique relies on the generation of a plasmid library that expresses all desired variants of a protein. Applying a selective pressure winnows the pool down to plasmids expressing variants with optimal function. High-throughput DNA sequencing is then used to measure the frequency of each variant during the selection process. Each variant is assigned a functional score based on its library frequency before selection compared to its library frequency after selection. Key to this process is the ability to generate full libraries of mutant proteins. Researchers from the Whitehead lab developed One pot saturation mutagenesis as a quick and easy technique that can be used to generate complex libraries of mutant plasmids ready for deep mutational scanning.

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Topics: Techniques

Lambda Red: A Homologous Recombination-based Technique for Genetic Engineering

Posted by Beth Kenkel on Dec 15, 2016 10:57:02 AM

Restriction enzyme cloning is the workhorse of molecular cloning; however, one of its biggest limitations is that sequence modifications can only be made at restriction enzyme cut sites. The lambda red system is an alternative method that can be used for cloning or genome engineering and is based on homologous recombination. It allows for direct modification of DNA within E. coli and is independent of restriction sites. The lambda red system is derived from the lambda red bacteriophage and its use as a genetic engineering tool is frequently called recombineering - short for homologous recombination-mediated genetic engineering.  It can be used to make an assortment of modifications: insertion and deletion of selectable and non-selectable sequences, point mutations or other small base pair changes, and the addition of protein tags. It also has the flexibility to modify the E. coli chromosome, plasmid DNA or BAC DNA. 

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Topics: Genome Engineering, Techniques, Microbiology

Plasmids 101: TOPO Cloning

Posted by Lianna Swanson on Oct 27, 2016 10:30:00 AM

Toposiomerase based cloning (TOPO cloning) is a DNA cloning method that does not use restriction enzymes or ligase, and requires no post-PCR procedures. Sounds easy right? The technique relies on the basic ability of complementary basepairs adenine (A) and thymine (T) to hybridize and form hydrogen bonds. This post focuses on "sticky end" TOPO (also called TOPO-TA) cloning; however, the TOPO cloning technique has also be adapted for blunt end cloning.

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Topics: Plasmid Technology, Plasmids 101, Techniques, Plasmid Cloning

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