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). Rpb2 is the second largest subunit of the RNA polymerase. This domain forms one of the two distinctive lobes of the Rpb2 structure. This domain is also known as the lobe domain. DNA has been demonstrated to bind to the concave surface of the lobe domain, and plays a role in maintaining the transcription bubble. Many of the bacterial members contain large insertions within this domain, as region known as dispensable region 1 (DRI).