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Monday October 22, 11:00 am, CIML lecture hall: Sylvain Moineau, Université Laval, Quebec: "Phages and CRISPR-Cas systems: The ongoing battle"

Abstract (...)

Abstract Fighting viruses is no easy task. Bacterial cells have survived phage attacks by evolving sophisticated defence strategies that enable them to thrive even in virus-rich ecosystems. Phages have also evolved counter-tactics to thwart such mechanisms, leading to a biological arms race. Clustered regularly interspaced short palindromic repeats (CRISPR) and their associated cas genes protect microbial cells against foreign nucleic acids such as phage genomes and plasmids. Bacterial CRISPR-Cas type II systems function by first incorporating short DNA ‘spacers’, derived from invading phage genomes or plasmid sequences, into a CRISPR array located in their genome. The bacterial CRISPR array is then transcribed and matured into short RNAs, which, by recruiting a Cas endonuclease, act as surveillance complexes that recognize and cleave subsequent invading matching DNA sequences. The cleavage occurs near a short motif, called the PAM, adjacent to the sequence targeted by the spacer. Exploiting this system has also resulted in the development of the much-publicized CRISPR-Cas9 technology for precise genome manipulation of various organisms. However, phages can bypass the protection provided by the CRISPR-Cas system through mutations of the CRISPR target in their genome or by the production of anti-CRISPR proteins (Acrs). These Acrs can also be used to fine-tune the activity of CRISPR-based genome editing tools. This seminar will recall the roles played by phages in the understanding of CRISPR-Cas systems. I will also highlight the recent discovery of new families of anti-CRISPR proteins and the of use of CRISPR-Cas9 technology for viral genome editing.
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