RNA polymerases catalyze the DNA dependent polymerization of RNA. Prokaryotes contain a single RNA polymerase compared to three in eukaryotes (not including mitochondrial. and chloroplast polymerases). This domain represents the hybrid binding domain and the wall domain. The hybrid binding domain binds the nascent RNA strand / template DNA strand in the Pol II transcription elongation complex. This domain contains the important structural motifs, switch 3 and the flap loop and binds an active site metal ion. This domain is also involved in binding to Rpb1 and Rpb3. Many of the bacterial members contain large insertions within this domain, as region known as dispensable region 2 (DRII).
Jiyao W et al.(2023). "The conserved domain database in 2023.",