engleski

Cas3 forms R-loops by pairing CRISPR RNA to homologous DNA sequences

Host cell CRISPR loci contain DNA sequence information required for resistance to invading viral or other genetic elements. In E. coli, CRISPR DNA is transcribed into RNA (pre-CrRNA) that is then processed by cascade proteins into mature crRNA: CrRNA is thought to facilitate interference with invading DNA ; but the mechanism for this RNA interference is not known. In addition to cascade proteins, Cas3 assists this interference pathway, but for reasons unknown. Here we report that E. coli cas3 catalyses pairing of CRISPR RNA with homologous DNA sequences in an efficient reaction that is dependent on a conserved motif in Cas3 protein and on a metal co-factor. We describe the biochemical characteristics of the Cas3 reaction in vitro and also some intriguing genetic interactions between cas3, stringent response regulators and topA rnhA mutants. We will discuss ideas that the essential role of cas3 in mediating immunity against invading DNA is part of a more general role for this protein in cells.

cas3; R-loop; CRISPR

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