<p>Prokaryotes contain a single RNA polymerase (RNAP) that is responsible for the transcription of all genes, while eukaryotes have three classes of RNAPs (I-III) with specific transcriptional roles. In eukaryotes, the RPB6 subunit is common to all three polymerases. RPB6 is involved in the initiation of transcription. Bacterial DNA-dependent RNAP contains a small subunit termed omega, where the complete RNAP composition is beta'-beta-alpha(I)-alpha(II)-omega. The bacterial omega subunit is homologous in sequence and structure to the eukaryotic RPB6 subunit; they also have similar functional roles, being able to promote RNA polymerase assembly, possibly through a latching mechanism [<cite idref="PUB00007936"/>].</p>