Schematic domain architecture of human Drosha and Dicer, DCL1 from A. thaliana (A.th.) and DrnA and DrnB from D. discoideum (D.d.) is shown. DsRBD (double stranded RNA binding domain), RIII (Ribonuclease III domain), HELICc (helicase superfamily c-terminal domain), DEXDc (Dead-like Helicases superfamily domain), PAZ (PAZ-domain), DUF283 (DUF283 domain). Human Drosha contains a region that is rich in prolines (P-rich site) as well as a region that is rich in serine and arginine (S/R-rich). DrnA and DrnB lack the Helicase domains, the DUF283 domain as well as the PAZ domain. DrnB exhibits a proline and serine rich (P/S-rich) region. Proteins and Domains are drawn to scale.