cl29917: RNA_pol_B_RPB2 Superfamily (this model, PSSM-Id:421949 is obsolete)
RNA polymerase beta subunit. RNA polymerases catalyse the DNA dependent polymerization of RNA. Prokaryotes contain a single RNA polymerase compared to three in eukaryotes (not including mitochondrial. and chloroplast polymerases). Each RNA polymerase complex contains two related members of this family, in each case they are the two largest subunits.The clamp is a mobile structure that grips DNA during elongation.