Tags: Protein.
DNA-directed RNA polymerase II subunit RPB1 is an enzyme that in humans is encoded by the POLR2A gene.This gene encodes the largest subunit of RNA polymerase II the polymerase responsible for synthesizing messenger RNA in eukaryotes. The product of this gene contains a carboxy terminal domain composed of heptapeptide repeats that are essential for polymerase activity. These repeats contain serine and threonine residues that are phosphorylated in actively transcribing RNA polymerase.