CTD Tyrosine Phosphorylation Impairs Termination Factor Recruitment to RNA Polymerase II

Don't Terminate Me! DNA transcription progresses through three phases—initiation, elongation, and termination—of messenger RNA chains. The transcribing enzyme, RNA polymerase (Pol) II, recruits factors that assist in each of these phases. Mayer et al. (p. 1723 ) now show that the C-terminal domain (CTD) of actively elongating Pol II is phosphorylated at conserved tyrosine residues. This modification impairs recruitment of termination factors. Factor exchange on the transcribing polymerase enzyme may be explained by an extended CTD code that is based on differential phosphorylation of the tyrosines and two well-characterized serine residues in the CTD.