 In "Drosophila" and "C. elegans", miRNA and siRNA are processed by distinct argonaute proteins and dicer enzymes.Three prime untranslated regions (3'UTRs) of messenger RNAs (mRNAs) often contain regulatory sequences that post-transcriptionally cause RNA interference.Such 3'-UTRs often contain both binding sites for microRNAs (miRNAs) as well as for regulatory proteins.