Molecular Biology Select

Argonaute proteins are central to RNA interference (RNAi) pathways. Loaded with small RNAs that serve as guides, Argonautes are key effectors of gene regulation, chromosome stability, and transposon control. One of the first activities associated with Argonaute proteins was a slicer function, that is, the endonucleolytic cleavage of target transcripts mediated by small interfering RNAs (siRNAs). Several studies now reveal an unexpected role for slicer in the biogenesis of microRNAs (miRNAs) and in miRNA-mediated silencing in mammals, a process previously thought to involve cleavage-independent mechanisms. Although these findings blur the distinction between miRNA- and siRNA-mediated silencing in mammals, another study provides new insight into the biochemical pathways that distinguish siRNAs from miRNAs in flies