This post was contributed by guest blogger Chris Richardson, a Postdoctoral Researcher in Jacob Corn’s lab.
CRISPR-Cas9 (Cas9) is an RNA-guided nuclease that targets and cuts genomic DNA. The interplay between Cas9 (which causes the breaks) and host cell DNA repair factors (which repair those breaks) makes Cas9 extremely effective as a genome editing reagent. This interplay falls into two broad categories and thus, causes two types of editing outcomes: Cas9 breaks repaired by the non-homologous end-joining (NHEJ) pathway disrupt target gene sequences (thus inactivating genes), while breaks repaired by homology directed repair (HDR) pathways can modify the sequence of a gene (thus altering its function). HDR is crucial for certain applications, for example, correcting the allele that causes sickle cell anemia. However, HDR occurs much less frequently than NHEJ and the efficiency of these editing reactions is low. Understanding the biological cause of this repair bias is a fascinating (and yet unanswered) question. Our recent paper (Richardson et al 2016) revealed some of the biophysical parameters that can influence the HDR/NHEJ decision.