Piwi-interacting RNA(piRNA):a Novel Class of Noncoding Small RNA

piRNA(Piwi-interacting RNA) is a novel class of small single strand RNA that were recently isolated from testes of the mammals, associate with PIWI proteins, and are organized into distinct genomic clusters. These RNAs are typically 30 nt long, strikingly different from microRNAs in their length, expression pattern, and genomic organization. piRNA has a role in RNA silencing via the formation of an RNA-induced silencing complex (RISC) with Piwi proteins, these piRNA complexes (piRCs) have been linked to transcriptional gene silencing of retrotransposons and other genetic elements in germ line cells, particularly those in spermatogenesis.Recent researches and progresses of piRNAs are reviewed.