A cellular function for the RNA-interference enzyme Dicer in the maturation of the let-7 small temporal RNA

The 21-nucleotide small temporal RNA (stRNA) let-7 regulates developmental timing in Caenorhabditis elegans and probably in other bilateral animals. W e present in vivo and in vitro evidence that in Drosophila melanogaster a d evelopmentally regulated precursor RNA is cleaved by an RNA interference-li ke mechanism to produce mature let-7 stRNA. Targeted destruction in culture d human cells of the messenger RNA encoding the enzyme Dicer, which acts in the RNA interference pathway, leads to accumulation of the let-7 precursor . Thus, the RNA interference and stRNA pathways intersect. Both pathways re quire the RNA-processing enzyme Dicer to produce the active small-RNA compo nent that represses gene expression.