CRISPR-Cas systems: from antiviral defense towards genome editing
14:00 - 15:00
Prof. Dr. Virginijus Siksnys
Institute of Biotechnology, Vilnius University
Max-Planck-Institut für biophysikalische Chemie (MPIBPC)
Large Seminar Room
Dr. Grazvydas Lukinavicius
Clustered regularly interspaced short palindromic repeats (CRISPR), together with CRISPR-associated genes (cas) constitute an adaptive microbial immune system which provides acquired resistance against viruses and plasmids. The CRISPR-Cas system hijacks short fragments of invasive DNA (spacers) and subsequently uses them as templates to generate specific small RNA molecules (crRNA) which combine with Cas proteins into effector complexes that trigger degradation of foreign nucleic acid, thereby preventing proliferation and propagation of invasive genetic elements. CRISPR systems are very diverse and differ in mechanism and assembly of effector complexes. In Type II systems, CRISPR-mediated immunity solely relies on the Cas9 protein. It binds a dual RNA into the effector complex, which then specifically cuts the matching target DNA, introducing a double strand break. The Cas9- guide RNA complex have been adopted as a robust and facile genome editing tool. For most applications typically one system that derived from Streptococcus pyogenes has been utilized. However, naturally occurring Cas9 orthologues are abundant in bacteria. To tap into this largely unexplored diversity for genome editing applications, we established a phylogeny-guided bioinformatics approach and developed a rapid biochemical screen for the rapid identification and characterization of the protospacer adjacent motif (PAM) and guide RNA requirement of new Cas9 proteins. This approach delivered Cas9s with novel PAM recognition that expand the genome editing capacity by increasing the sequence space targetable by Cas9.