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 was at one point experimentally difficult to determine, but it has been demonstrated to be a heterotrimer of two DGCR8 proteins and one Drosha.
In addition to the minimal catalytically active microprocessor components, other 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.