In a previous post from our Plasmids 101 series, we learned how the Cre-loxP recombination system can be used to induce site-specific recombination events, and that the orientation of the flanking loxP sites directs the Cre recombinase to invert, translocate, or excise a DNA fragment. The availability of both wild-type and mutant loxP sites has allowed scientists to leverage this system in new, creative ways. Today’s post will focus on one such strategy--the FLEx switch--which utilizes recombination elements to turn off expression of one gene, while simultaneously turning on the expression of another!

This post was contributed by guest bloggers Albert Cheng and Mark Wanner.

CRISPR-Cas9 offers a leap forward for genome editing, providing researchers with greatly enhanced accuracy, efficiency, and versatility. It has led to a tremendous acceleration of biomedical research, allowing for the modeling of human disease mutations in experimental model systems with previously unthinkable speed and precision. Furthermore, the ability to excise detrimental mutations and introduce functional sequences—as is being investigated with dystrophin/Duchenne muscular dystrophy at this time—is potentially transformative for human clinical care for some Mendelian diseases.

CRISPR has quickly become the preferred system for genome engineering due to its simplicity, as it requires only Cas9 and a guide RNA (gRNA).  Choosing the correct method to deliver both Cas9 and gRNAs to your target cells is absolutely critical as failure to adequately express either component will result in a failed experiment.  In our previous blog post entitled “CRISPR 101 - Mammalian Expression Systems and Delivery Methods” we provided a general overview of the most common ways in which you can deliver Cas9 and gRNAs to your target cells and discussed a few key advantages and disadvantages of each method. In this blog post, we will go into greater detail about why and how Cas9/gRNA Ribonucleoprotein complexes (Cas9 RNPs) are being used for genome engineering experiments and provide a general framework for getting started with Cas9 RNPs in your research.

This post was contributed by guest blogger Erik L. Snapp.

Stop using EGFP/GFP for fusion proteins! Despite multiple studies in high profile journal articles, many researchers remain unaware that EGFP/GFP is prone to forming noncovalent dimers. This property of EGFP can lead to significant artifacts.

If you're using green fluorescent protein or Enhanced Green Fluorescent Protein (GFP/EGFP) for a transcriptional reporter or as a general cytoplasmic label of cells, there's no problem. You're OK. However, if you fuse your protein of interest (POI) to GFP to study the protein's behavior in cells, in solution or something in between, you are using a tag with a serious drawback. The standard EGFP plasmid that used to be sold by Clontech and is in a freezer box in just about every lab in the world, is not inert. In all seriousness, EGFP/GFP has a real nontrivial propensity to noncovalently dimerize. That means that your POI fused to GFP or another fluorescent protein (FP) could be forming dimers in cells. Why should you care? Three simple ways a dimeric FP could ruin your day (and experiment) are listed below. Solutions to avoid these all too common issues follow.

This post was contributed by guest blogger Jessica Polka, a Postdoctoral Research Fellow with Pamela Silver. 

Most types of biological motion (whether endocytosis, vesicle trafficking, or muscle contractions) are produced by orchestrated movements of networks of proteins consuming molecular fuel sources. While the importance of understanding these complex processes can’t be overstated, we can also learn a lot from Nature’s simpler solutions to transmitting forces over long distances. For instance, how much force can be generated by conformational changes in proteins? How can information propagate through a structured material over a long distance? And can we understand such a structure well enough to engineer it to suit our purposes?