Requirement for phosphorylation of RNA polymerase II C-terminal domain in transcription is both transcript length and promoter dependent.

RNA polymerase II exists in both phosphorylated and nonphosphorylated forms. The interconversion between these two forms is suggested to be the molecular switch that regulates the transition from transcription initiation to elongation. Here, the ATP analogue H8 is used as a CTD kinase inhibitor to study the role of CTD phosphorylation in transcription with a HeLa nuclear extract in vitro. The results demonstrate that (i) CTD phosphorylation is not required for transcription of the promoter proximal region from TATA containing promoters, (ii) the primary role of CTD phosphorylation is to promote productive elongation, and (iii) the contribution of CTD phosphorylation to transcription differs among TATA containing promoters as well as between TATA less and TATA containing promoters.