Structural insight into recognition of phosphorylated threonine‐4 of RNA polymerase II C‐terminal domain by Rtt103p

Abstract

Phosphorylation patterns of the C‐terminal domain ( CTD ) of largest subunit of RNA polymerase II (called the CTD code) orchestrate the recruitment of RNA processing and transcription factors. Recent studies showed that not only serines and tyrosines but also threonines of the CTD can be phosphorylated with a number of functional consequences, including the interaction with yeast transcription termination factor, Rtt103p. Here, we report the solution structure of the Rtt103p CTD ‐interacting domain ( CID ) bound to Thr4 phosphorylated CTD , a poorly understood letter of the CTD code. The structure reveals a direct recognition of the phospho‐Thr4 mark by Rtt103p CID and extensive interactions involving residues from three repeats of the CTD heptad. Intriguingly, Rtt103p's CID binds equally well Thr4 and Ser2 phosphorylated CTD . A doubly phosphorylated CTD at Ser2 and Thr4 diminishes its binding affinity due to electrostatic repulsion. Our structural data suggest that the recruitment of a CID ‐containing CTD ‐binding factor may be coded by more than one letter of the CTD code. image Phosphorylation of RNA Pol II CTD recruits several transcription and RNA processing factors, including yeast transcription termination factor Rtt103p. This study provides the structural basis for how the CTD ‐interacting domain of Rtt103p recognizes pT hr4 and pS er2 CTD. Rtt103p CID binds equally well Thr4 and Ser2 phosphorylated CTD whereas a doubly phosphorylated CTD at Ser2 and Thr4 diminishes its binding affinity. The structure of Rtt103p CID bound to Thr4 phosphorylated CTD reveals a direct recognition of the pT hr4 mark. The same interaction pocket of Rtt103p can read two different phosphorylation patterns of the CTD , pS er2 and pT hr4, using the same structural mechanism.