Dicing defence in bacteria

摘要

Viruses and mobile genetic elements such as plasmids pose a threat to the genomic integrity of organisms from all domains of life, whether they be eukary-otes (organisms with discrete cell nuclei, for example plants and animals), bacteria or archaea. Some of the most exciting findings made over the past 15 years have been the RNA-based defence systems of eukaryotes (RNA interference, or RNAi) and of bacteria and archaea (CRISPR systems). In both cases, RNA transcripts are processed by endonucle-ase enzymes into short guide RNAs that then target invaders that have complementary nucleic-acid sequences. The Dicer endonucle-ase is essential for RNAi processing~1. On page 602 of this issue, Deltcheva et al.~2 describe a processing pathway for CRISPR RNA that has intriguing similarities to the RNAi pathway, including dependence on the bacterial equivalent of Dicer, RNase III. A frans-acting RNA, tracrRNA, targets the cleavage process that ultimately produces mature guide RNAs.