RNA polymerases catalyse the DNA dependent polymerisation of RNA. Prokaryotes contain a single RNA polymerase compared to three in eukaryotes (not including mitochondrial. and chloroplast polymerases). This domain forms one of the two distinctive lobes of the Rpb2 structure. This domain is also known as the protrusion domain [1]. The other lobe (Pfam:PF04561) is nested within this domain.

1: RNA polymerase II of Drosophila. Relation of its 140,000 Mr subunit to the beta subunit of Escherichia coli RNA polymerase. Falkenburg D, Dworniczak B, Faust DM, Bautz EK; J Mol Biol 1987;195:929-937. PMID:3116266

2: Structural basis of transcription: RNA polymerase II at 2.8 angstrom resolution. Cramer P, Bushnell DA, Kornberg RD; Science 2001;292:1863-1876. PMID:11313498