Microprocessor complex

The Microprocessor complex is a protein complex involved in the early stages of processing microRNA (miRNA) in animal cells. The complex is minimally composed of the ribonuclease enzyme Drosha and the RNA-binding protein DGCR8 (also known as Pasha) and cleaves primary miRNA substrates to pre-miRNA in the cell nucleus.

The Microprocessor complex consists minimally of two proteins: Drosha, a ribonuclease III enzyme; and DGCR8, a double-stranded RNA binding protein. (DGCR8 is the name used in mammalian genetics, abbreviated from "DiGeorge syndrome critical region 8"; the homologous protein in model organisms such as flies and worms is called Pasha, for Partner of Drosha.) The stoichiometry of the minimal complex has been experimentally difficult to determine, but has been determined by biochemical analysis, single-molecule experiments, and X-ray crystallography to be a heterotrimer of two DGCR8 proteins to one Drosha.

In addition to the minimal catalytically active Microprocessor components, additional cofactors such as DEAD box RNA helicases and heterogeneous nuclear ribonucleoproteins may be present in the complex to mediate the activity of Drosha. Some miRNAs are processed by Microprocessor only in the presence of specific cofactors.

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