CRISPR-Cas, the adaptive immune system of Streptococcus thermophilus
Bacteria and archaea have developed multiple defence strategies against phages and plasmids. Among them, clustered regularly interspaced short palindromic repeats (CRISPR) loci, together with cas (CRISPR associated) genes, form the CRISPR-Cas immune system. CRISPR loci are composed of repeats separated by short stretches of variable DNA called spacers.
Using the dairy bacterium Streptococcus thermophilus as a model, we demonstrated that the CRISPR loci evolve through the acquisition of new spacers, derived from phage or plasmid sequences. A CRISPR transcript is then produced and cleaved within the repeats by Cas protein(s) with or without other host proteins to produce smaller RNAs. These small mature RNAs and Cas proteins guide and cleave in a sequence-specific manner the invading DNA to ensure cell defense.
Altogether, the CRISPR-Cas immune system is remarkably adapted to rapidly cleave invading DNA. It can be exploited to generate phage-resistant bacterial strains as well as for genome editing. This seminar will present the latest developments in this exciting area.