A non-essential component of RNA polymerase (RNAP) (Probable). Has a similar structure to bacteriophage T7 protein Gp2 (AC P03704), which is known to bind to RNAP in the DNA binding-cleft. Unlike Gp2 however, this protein does not inhibit transcription inititation (PubMed:25092033). a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Monomer (PubMed:25092033). RNAP is composed of a core of 2 alpha, a beta and a beta' subunit. The core is associated with a delta subunit, and at least one of epsilon or omega. When a sigma factor is associated with the core the holoenzyme is formed, which can initiate transcription (By similarity). Belongs to the RNA polymerase subunit epsilon family.