Gene silencing is an adaptive defence mechanism against viruses first identified in plants. RNA interference is a gene-silencing event triggered by a double-stranded (ds) RNA and it involves the generation of small RNA segments that guide mRNA destruction. In July Cell Alla Grishok and colleagues from the Howard Hughes Medical Institute, University of Massachusetts Medical School Worcester, Massachusetts show that a common processing machinery produces guide RNAs that mediate both RNA interference and endogenous gene regulation.

In Caenorhabditis elegans, lin-4 and let-7 encode small temporal RNAs (stRNAs) of 22 nt which regulate the larval to adult development. Grishok et al. found that RNA interference related genes are involved in the expression and activity of these stRNA genes. The activities of two C. elegans homologs of rde-1 — alg-1 and alg-2 — are essential for the proper function of the lin-4 and let-7 stRNA pathways. In addition,...