How an mRNA capping enzyme reads distinct RNA polymerase II and Spt5 CTD phosphorylation codes

作者：Doamekpor Selom K; Sanchez Ana M; Schwer Beate; Shuman Stewart^*; Lima Christopher D

来源：Genes & Development, 2014, 28(12): 1323-1336.

DOI：10.1101/gad.242768.114.

• transcription
• mRNA capping
• regulation
• Spt5
• RNA polymerase II

Interactions between RNA guanylyltransferase (GTase) and the C-terminal domain (CTD) repeats of RNA polymerase II (Pol2) and elongation factor Spt5 are thought to orchestrate cotranscriptional capping of nascent mRNAs. The crystal structure of a fission yeast GTase center dot Pol2 CTD complex reveals a unique docking site on the nucleotidyl transferase domain for an 8-amino-acid Pol2 CTD segment, S5PPSYSPTS5P, bracketed by two Ser5-PO4 marks. Analysis of GTase mutations that disrupt the Pol2 CTD interface shows that at least one of the two Ser5-PO4-binding sites is required for cell viability and that each site is important for cell growth at 37 degrees C. Fission yeast GTase binds the Spt5 CTD at a separate docking site in the OB-fold domain that captures the Trp4 residue of the Spt5 nonapeptide repeat T(1)PAW(4)NSGSK. A disruptive mutation in the Spt5 CTD-binding site of GTase is synthetically lethal with mutations in the Pol2 CTD-binding site, signifying that the Spt5 and Pol2 CTDs cooperate to recruit capping enzyme in vivo. CTD phosphorylation has opposite effects on the interaction of GTase with Pol2 (Ser5-PO4 is required for binding) versus Spt5 (Thrl-PO4 inhibits binding). We propose that the state of Thrl phosphorylation comprises a binary "Spt5 CTD code" that is read by capping enzyme independent of and parallel to its response to the state of the Pol2 CTD.

• 出版日期2014-6-15