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Plasmids 101: E. coli Strains for Protein Expression

Posted by Julian Taylor-Parker on Feb 10, 2015 10:06:00 AM

In a previous Plasmids 101 blog, we reviewed the salient features of several popular strains of E. coli for DNA propagation. While great for cloning purposes, these E. coli strains are not usually well suited for recombinant protein expression. Many challenges can arise when over-expressing a foreign protein in E. coli. We will review the potential pitfalls of recombinant protein expression and some of the most popular commercial strains designed to avoid them.

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Topics: Lab Tips, Plasmids 101

Plasmids 101: Cre-lox

Posted by A Max Juchheim on Jan 13, 2015 10:47:00 AM

In previous posts for our Plasmids 101 series, we examined a number of important plasmid elements – promoters, origins of replication, protein tags, and antibiotic resistance markers (just to name a few). In this edition, we’re going to take a look at a very interesting tool that can be used for creating (excuse the pun) specific, targeted DNA modifications in transgenic animals, embryonic stem cells, and/or tissue-specific cell types: Cre-lox recombination.

What is Cre-lox?

The Cre-lox system is a technology that can be used to induce site-specific recombination events. The system consists of two components derived from the P1 bacteriophage: the Cre recombinase and a loxP recognition site. The P1 bacteriophage uses these components as part of its natural viral lifecycle, and researchers have adapted the components for use in genome manipulation.

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Topics: Plasmid Technology, Plasmid Elements, Plasmids 101

Plasmids 101: Protein tags

Posted by Eric J. Perkins on Dec 11, 2014 11:26:00 AM

Protein tags are usually smallish peptides incorporated into a translated protein. As depicted in the accompanying cartoon, they have a multitude of uses including (but not limited to) purification, detection, solubilization, localization, or protease protection. Thus far Plasmids 101 has covered GFP and its related fluorescent proteins, which are sometimes used as tags for detection; however, those are just one (admittedly large) class of common fusion protein tags. Biochemists and molecular biologists who need to overexpress and purify proteins can face any number of technical challenges depending on their protein of interest. After several decades of trying to address these challenges, researchers have amassed a considerable molecular tool box of tags and fusion proteins to aid in the expression and purification of recombinant proteins.

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Topics: Plasmid Elements, Plasmids 101

Plasmids 101: Common Lab E. coli Strains

Posted by Matthew Ferenc on Nov 7, 2014 9:56:00 AM

This post was updated on Nov 14, 2017.

You've worked hard designing your plasmid – you carefully selected the optimal promoter for your gene of interest, painstakingly cloned into the perfect empty backbone, made sure to add the right tags to your gene, and may have even put a fluorescent protein downstream, separated by an IRES element. You did a lot of work! But let’s take a moment to recognize your little prokaryotic minions that carried out the labor-intensive process of replicating your new plasmid: the Escherichia coli bacteria.

It’s hard to count the number of different commercial strains of E. coli currently available  a quick Google search suggests there are hundreds. This only includes general lab strains designed for subcloning or protein expression. If you were to include customized strains, the number is probably in the thousands! The goal of this article is to provide enough background for you to distinguish the features of any common lab strain and determine whether it is appropriate for propogating your plasmid or carrying out your experiment.

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Topics: Lab Tips, Plasmids 101

ICYMI: Addgene’s Plasmids 101 eBook

Posted by Marcy Patrick on Oct 2, 2014 1:25:00 PM

We'd like to thank all of the contributing Addgenies that made this eBook possible: Melina Fan, Matthew Ferenc, Larissa Haliw, A. Max Juchheim, Caroline LaManna, Margo Monroe, Kendall Morgan, Jason Niehaus, Marcy Patrick, Lianna Swanson, Julian Taylor-Parker

We'd also like to thank our guest contributor: Gal Haimovich of greenfluorescentblog.org for helping us explain why things glow!

Addgene's Plasmids 101 eBook is here: Enjoy more time developing clever experiments and less time researching basic plasmid features – download the Addgene Plasmids 101 eBook!

Our goal was to create a one-stop reference guide for plasmids. We’ve combined our Plasmids 101 blog posts from the last year with some additional resources to create one downloadable PDF you can save to your desktop for easy reference. Highlights include our guide to fluorescent proteins, information about promoters and ORIs, and tips for naming your plasmids.  

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Topics: Plasmid Elements, Lab Tips, Plasmids 101

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