Mapping the C Terminal Domain of RNA Polymerase II by UVPD Mass Spectrometry

University Of Texas At Austin, Austin TX

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Abstract

DESCRIPTION (provided by applicant): Transcription and regulation of gene expression are temporally mediated by modification of the C terminal domain (CTD) of subunit 1 of RNA polymerase II. The combinatorial phosphorylation pattern of the CTD, a 52 consensus repeat of a YSPTSPS heptad, coordinates RNA biogenesis in the transcription cycle. Progress in resolving the regulatory roles of the CTD has been impeded by lack of suitable methods for site-specific and quantitative mapping of CTD phosphorylation, an issue that directly ties structure to function. This proposal addresses this challenge by the development of ultraviolet photodissociation (UVPD) mass spectrometry to map the phosphorylation pattern and occupancy of the CTD in conjunction with label-free quantitation. The three proposed aims include: (1) Analysis of the combinatorial phosphorylation pattern of the CTD using 193 nm UVPD. The ~26 kDa CTD peptide of RNA pol II will be isolated, digested by Proteinase K, and the resulting peptides analyzed by nanoLC-UVPD-MS in the negative mode. Both the phosphorylation sites and occupancies will be characterized. (2) Quantitative analysis of global CTD phosphoryl occupancy and exposure to cell stressors. Changes in the CTD code as a function of particular cell stressors, including heat shock, exposure to salt, dithiothreitol, lipopolysaccharides (LPS), sorbitol or hydrogen peroxide, will be elucidated by label-free quantitation. (3) Quantitative analysis of global CTD phosphoryl occupancy between a control and a yeast strain with a functionally deficient Ssu72 phosphatase. Ssu72 displays specific phosphatase activity toward Ser2 and Ser5 of the CTD heptad repeat, two sites that play a critical role in the temporal regulation of transcription. RNA pol II from Ssu72-deficient and control yeast strains will be harvested, digested with trypsin, and processed to isolate the CTD peptides. The resulting phosphorylated peptides, which will differ in occupancy and abundance for each cell state, will be evaluated by label-free quantitation. This application of innovative UVPD technology will provide critical insight into the role of CTD phosphorylation in transcriptional processing.