<p>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 [<cite idref="PUB00003220"/>]. The other lobe, RNA polymerase Rpb2, domain 2, is nested within this domain.</p>