Werner-Allen, J.W., Lee, C.J., Liu, P., Nicely, N.I., Wang, S., Greenleaf, A.L., Zhou, P. (2011). cis-Proline-mediated Ser(P)5 dephosphorylation by the RNA polymerase II C-terminal domain phosphatase Ssu72.  J. Biol. Chem. 286(7): 5717--5726.

FBrf0214135

Research paper

RNA polymerase II coordinates co-transcriptional events by recruiting distinct sets of nuclear factors to specific stages of transcription via changes of phosphorylation patterns along its C-terminal domain (CTD). Although it has become increasingly clear that proline isomerization also helps regulate CTD-associated processes, the molecular basis of its role is unknown. Here, we report the structure of the Ser(P)(5) CTD phosphatase Ssu72 in complex with substrate, revealing a remarkable CTD conformation with the Ser(P)(5)-Pro(6) motif in the cis configuration. We show that the cis-Ser(P)(5)-Pro(6) isomer is the minor population in solution and that Ess1-catalyzed cis-trans-proline isomerization facilitates rapid dephosphorylation by Ssu72, providing an explanation for recently discovered in vivo connections between these enzymes and a revised model for CTD-mediated small nuclear RNA termination. This work presents the first structural evidence of a cis-proline-specific enzyme and an unexpected mechanism of isomer-based regulation of phosphorylation, with broad implications for CTD biology.

PMC3037684 (PMC) (EuropePMC)