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Some Like it Hot: Thermostable GeoCas9

Posted by Beth Kenkel on Sep 14, 2017 8:40:16 AM

Cas9 is the genome editing tool of choice for a number of model organisms: mammalian cells, yeast, drosophila, plants, worms, zebrafish, frogs, some bacteria; but not thermophilic (high heat loving) bacteria. Until recently the only available Cas9 proteins were isolated from mesophilic (medium heat loving) bacteria, such as Streptococcus pyogene’s SpCas9. These Cas9 proteins don’t work well at high temperatures, so to use them in thermophiles, bacteria must be grown at lower temps. This approach only works for facultative thermophiles (high OR medium heat loving), but not obligate thermophiles. However, the recent discovery of GeoCas9 by the Doudna lab has opened up the field of thermophilic bacteria to CRISPR/Cas9 genome editing.

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Topics: Genome Engineering, CRISPR

How to Design Your gRNA for CRISPR Genome Editing

Posted by Guest Blogger on May 3, 2017 11:00:00 AM

This Post was updated on May 3, 2017 with additional information and resources. 

This post was contributed by guest blogger, Addgene Advisory Board member, and Associate Director of the Genetic Perturbation Platform at the Broad Institute, John Doench.

CRISPR technology has made it easier than ever both to engineer specific DNA edits and to perform functional screens to identify genes involved in a phenotype of interest. This blog post will discuss differences between these approaches, as well as provide updates on how best to design gRNAs. You can also find validated gRNAs for your next experiment in Addgene's Validated gRNA Sequence Datatable.

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Topics: Plasmid How To, Genome Engineering, Lab Tips, CRISPR

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: Knockout/Knock-In Plasmids

Posted by Benoit Giquel on Dec 1, 2016 10:30:00 AM

One of the most powerful strategies to investigate a gene's function is to inactivate, or "knockout", the gene by replacing it or disrupting it with an piece of DNA designed in the lab. Specially constructed plasmids can be used to replace genes in yeast, mice, or Drosophila through homologous recombination. The concept is simple: deliver a template with a modified version of the targeted sequence to the cell which will recombine the template with the endogenous gene. Here, we'll describe the techniques and the plasmids used to inactivate specific genes in mammalian cells. Despite the popularity of CRISPR-based knockout/knock-in systems, these systems remain valuable, especially in cases where CRISPR cannot be used (e.g. there are no suitable PAM sequences nearby or your gene of interest is difficult to target specifically with a gRNA). Be sure to keep these techniques in mind when choosing a knockout strategy!

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Topics: Plasmid How To, Genome Engineering, Plasmids 101

Single Base Editing with CRISPR

Posted by Mary Gearing on Aug 16, 2016 10:30:00 AM

This post was updated on Nov 27, 2017.

When we talk about CRISPR applications, one negative always comes up: the low editing efficiency of homology-directed repair (HDR). Compared to non-homologous end joining, HDR occurs at a relatively low frequency, and in nondividing cells, this pathway is further downregulated. Rather than try to improve HDR, Addgene depositor David Liu’s lab created new Cas9 fusion proteins that act as base editorsThese fusions contain dCas9 or Cas9 nickase and a cytidine deaminase, and they can convert cytosine to uracil without cutting DNA. Uracil is then subsequently converted to thymine through DNA replication or repair. Later work has improved base editor targeting flexibility and specificity. New adenine base editors also allow you to change adenine to inosine, which is then converted to guanine.

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Topics: Genome Engineering, CRISPR

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