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 entry, domain 4, represents the funnel domain. The funnel domain contains the binding site for some elongation factors [<cite idref="PUB00002975"/>, <cite idref="PUB00008731"/>].