Bacterial RNA polymerase subunit ω and eukaryotic RNA polymerase subunit RPB6 ave sequence, structural, and functional homologs and promote RNA polymerase assembly

Bacterial DNA-dependent RNA polymerase (RNAP) has subunit composition beta'beta alpha (1)alpha (11)omega The role of omega has been unclear. We show that w is homologous in sequence and structure to RPB6, an essential subunit shared in eukaryotic RNAP I, II, and III. In Escherichia coli, overproduction of omega suppresses the assembly defect caused by substitution of residue 1362 of the largest subunit of RNAP, beta'. In yeast, overproduction of RPB6 suppresses the assembly defect caused by the equivalent substitution in the largest subunit of RNAP II, RPB1. High-resolution structural analysis of the omega-beta' interface in bacterial RNAP, and comparison with the RPB6-RPB1 interface in yeast RNAP II, confirms the structural relationship and suggests a latching mechanism for the role of omega and RPB6 in promoting RNAP assembly.