Drosha

Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the DROSHA (formerly RNASEN) gene.

Function

Members of the ribonuclease III superfamily of double-stranded (ds) RNA-specific endoribonucleases participate in diverse RNA maturation and decay pathways in eukaryotic and prokaryotic cells. The RNase III Drosha is the core nuclease that executes the initiation step of microRNA (miRNA) processing in the nucleus.

The microRNAs thus generated are short RNA molecules that regulate a wide variety of other genes by interacting with the RNA-induced silencing complex (RISC) to induce cleavage of complementary messenger RNA (mRNA) as part of the RNA interference pathway. A microRNA molecule is synthesized as a long RNA primary transcript known as a pri-miRNA, which is cleaved by Drosha to produce a characteristic stem-loop structure of about 70 base pairs long, known as a pre-miRNA. Drosha exists as part of a protein complex called the Microprocessor complex, which also contains the double-stranded RNA binding protein Pasha (also called DGCR8). Pasha is essential for Drosha activity and is capable of binding single-stranded fragments of the pri-miRNA that are required for proper processing.