C2c2 is a single-component programmable RNA-guided RNA-targeting CRISPR effector

INTRODUCTION Almost all archaea and about half of bacteria possess clustered regularly interspaced short palindromic repeat (CRISPR)–CRISPR-associated genes (Cas) adaptive immune systems, which protect microbes against viruses and other foreign DNA. All functionally characterized CRISPR systems have been reported to target DNA, with some multicomponent type III systems also targeting RNA. The putative class 2 type VI system, which has not been...