Pol IV and RDR2: A two-RNA-polymerase machine that produces double-stranded RNA

Abstract

A tunnel between RNA polymerases Eukaryotes encode five multiple-subunit, DNA-dependent RNA polymerases, of which Pol I, Pol II, and Pol III function as single units to produce cellular single-stranded RNA. The plant-specific Pol IV forms a complex with RDR2 (an RNA-dependent RNA polymerase) to produce double-stranded precursors of small interfering RNA essential for genomic DNA methylation. Huang et al . determined the cryo–electron microscopy structures of the Pol IV-RDR2 complex. The structures show that Pol IV and RDR2 connect their active centers through an inner RNA transfer channel and that Pol IV reverses transcription direction and hands over its transcript directly through the channel to RDR2 for the production of the second strand of the double-stranded RNA. —DJ