<p>RNA polymerases (<db_xref db="EC" dbkey="2.7.7.6"/>) catalyse the DNA dependent polymerisation of RNA.Prokaryotes contain a single RNA polymerase compared to three in eukaryotes (notincluding mitochondrial. and chloroplast polymerases). This domain represents thehybrid binding domain and the wall domain [<cite idref="PUB00008731"/>]. Thehybrid-binding domain binds the nascent RNA strand / template DNA strand in thePol II transcription elongation complex. This domain contains the important structuralmotifs, switch 3 and the flap loop and binds an active site metal ion [<cite idref="PUB00008731"/>]. This domain is also involved in binding to Rpb1 and Rpb3[<cite idref="PUB00008731"/>]. Many of the bacterial members contain large insertionswithin this domain, which is known as dispensable region 2 (DRII).</p>