Regulated phosphorylation of the RNA polymerase II C-terminal domain (CTD).

The largest subunit of RNA polymerase II has an intriguing feature in its carboxyl-terminal domain (CTD) that consists of multiple repeats of an evolutionary conserved motif of seven amino acids. CTD phosphorylation plays a pivotal role in controlling mRNA synthesis and maturation. In exponentially growing cells, the phosphate turnover on the CTD is fast; it is blocked by common inhibitors of transcription, such as 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole and actinomycin D. Transcription-independent changes in CTD phosphorylation are observed at critical developmental stages, such as meiosis and early development.