Small RNAs and proteins in RNA silencing pathways

Small regulatory RNAs, including siRNA (short interfering RNA), miRNA (microRNA), piRNA (piwi interacting RNA), and hsRNA (heterochromatin associated small RNA), have been the hot frontier of life sciences in the past few years, and it is becoming more and more apparent that these small molecules have key regulatory functions. Small RNAs trigger various forms of sequence specific gene silencing, commonly referred to as RNA silencing, such as RNA interference (RNAi), translational repression, and heterochromatin formation in all higher eukaryotes and play important roles in cellular processes as diverse as development, stress response, or transposon silencing. Soon after the discovery of small regulatory RNAs, members of the RNase III family and Argonaute protein family, some RNA binding proteins, and etc., were identified as their major cellular protein interactors and involved in the biogenesis and various cellular functions of small RNAs. This review summaries the understanding of the structures and functions of the important components in small RNA-induced gene-silencing pathways.