Exonucleolytic Degradation of Double-Stranded RNA by an Activity in Xenopus laevis Germinal Vesicles

We have identified, in extracts from Xenopus laevis germinal vesicles, a 5′ exonuclease activity that cleaves double-stranded RNA (dsRNA). Features of the 5′ ends of dsRNAs determine whether the strands are symmetrically or asymmetrically degraded. The activity hydrolyzes in the 5′ to 3′ direction, releasing 5′-mononucleotides processively, favoring strands with 5′-monophosphate termini; molecules with capped ends are resistant to digestion. Because of its ability to processively digest dsRNA to mononucleotides, we have named the exonuclease Chipper, which could cooperate or compete with Dicer (an endonuclease that produces molecules with a 5′-phosphate) in the processing of dsRNA.