Repeat associated small interfering RNA (rasiRNA) is a class of small RNA that is involved in the RNA interference (RNAi) pathway. RasiRNA are in fact Piwi-interacting RNAs (piRNAs), which are small RNA molecules that interact with Piwi proteins. Piwi proteins are a clade of the  Argonaute family of proteins. In the germline, RasiRNA is involved in establishing and maintaining heterochromatin structure, controlling transcripts that emerge from repeat sequences, and silencing transposons and retrotransposons.