RNA引导免疫的病毒起源

Ancient viral warfare could be at the root of modern class 1 CRISPR bacterial defense systems Jack P. K. Bravo Bacteria use clustered regularly interspaced short palindromic repeats (CRISPR)–Cas systems as defense against viruses. After infection, CRISPR systems capture pieces of invading nucleic acids and insert them into the bacterial genome. These sequences provide genetic memory of previous infections and are later copied into guide RNAs that direct Cas enzymes to matching viral nucleic acids. Class 2 CRISPR systems rely on a single Cas enzyme, whereas class 1 systems use multiprotein assemblies. The origins of class 2 systems are well understood (1, 2), but those of class 1 systems have remained elusive. …