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MudPIT analysis of proteins interacting with Saccharomyces cerevisiae RNA Polymerase II HA-Rpb1 C-Terminal Domain

ABSTRACT: The carboxy-terminal domain (CTD) of Rpb1, the largest component of the 12-subunit RNA polymerase II, consists of repeating Y1S2P3T4S5P6S7 heptapeptides (26 repeats in budding yeast). Each stage of transcription relies on the ordered recruitment and exchange of specific protein complexes that act on RNA polymerase II, its nascent transcripts, and the underlying chromatin. This dynamic process is orchestrated via patterned post-translational modifications of the CTD. To characterize the role of phosphorylation on Thr4, we examined the effect of Rpb1 alleles in which Thr4 was substituted with an alanine (T4A) or the phospho-mimic glutamate (T4E). Substitutions were made across all heptad repeats of the CTD. We affinity purified HA-tagged Rpb1 from Saccharomyces cerevisiae strains bearing WT, T4A, and T4E CTDs. A control strain (Z26) lacking the HA-tagged Rpb1 was subjected to an identical affinity enrichment procedure. Three biological replicates were acquired for each type of affinity purification and analyzed independently. After TCA-precipitation, proteins were urea-denatured, reduced, alkylated, then digested with endoproteinase LysC followed by trypsin. The resulting peptide mixtures were analyzed by Multidimensional Protein Identification Technology (MudPIT). Label-free quantitative proteomics was used to identify and quantify the relative abundance of affinity-enriched complexes.

INSTRUMENT(S): LTQ

ORGANISM(S): Saccharomyces Cerevisiae (ncbitaxon:4932)

SUBMITTER: Laurence Florens

PROVIDER: MSV000080573 | MassIVE | Fri Feb 24 15:12:00 GMT 2017

SECONDARY ACCESSION(S): PXD005967

REPOSITORIES: MassIVE

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Project description:RPB1, the largest subunit of RNA polymerase II, contains a highly modifiable C-terminal domain (CTD) that consists of variations of a consensus heptad repeat sequence (Y1S2P3T4S5P6S7). The consensus CTD repeat motif and tandem organization represent the ancestral state of eukaryotic RPB1, but across eukaryotes CTDs show considerable diversity in repeat organization and sequence content. These differences may reflect lineage-specific CTD functions mediated by protein interactions. Mammalian CTDs contain eight non-consensus repeats with a lysine in the seventh position (K7). Posttranslational acetylation of these sites was recently shown to be required for proper polymerase pausing and regulation of two growth factor-regulated genes. To investigate the origins and function of RPB1 CTD acetylation (acRPB1), we computationally reconstructed the evolution of the CTD repeat sequence across eukaryotes and analyzed the evolution and function of genes dysregulated when acRPB1 is disrupted. Modeling the evolutionary dynamics of CTD repeat count and sequence content across diverse eukaryotes revealed an expansion of the CTD in the ancestors of Metazoa. The new CTD repeats introduced the potential for acRPB1 due to the appearance of distal repeats with lysine at position seven. This was followed by a further increase in the number of lysine-containing repeats in developmentally complex clades like Deuterostomia. Mouse genes enriched for acRPB1 occupancy at their promoters and genes with significant expression changes when acRPB1 is disrupted are enriched for several functions, such as growth factor response, gene regulation, cellular adhesion, and vascular development. Genes occupied and regulated by acRPB1 show significant enrichment for evolutionary origins in the early history of eukaryotes through early vertebrates. Our combined functional and evolutionary analyses show that RPB1 CTD acetylation was possible in the early history of animals, and that the K7 content of the CTD expanded in specific developmentally complex metazoan lineages. The functional analysis of genes regulated by acRPB1 highlight functions involved in the origin of and diversification of complex Metazoa. This suggests that acRPB1 may have played a role in the success of animals. We used a HA-tagged mouse RPB1 construct in which all K7 residues were substituted with arginines (8KR). This mutation resembles unacetylated lysines by conserving the positive charge at these positions, but preventing acetylation. To examine the potential functions of K7 acetylation in regulating gene expression, we stably expressed wildtype or 8KR HA-RPB1 in murine NIH/3T3 fibroblasts and cultured these cells in media containing α-amanitin. Both were expressed at equivalent levels, but acetylation was present only in wildtype, and not mutant HA-RPB1. We then performed gene expression profiling using the Affymetrix Mouse Gene 1.0 ST microarray with three biological replicates.

Project description:Eukaryotic RNA polymerase II (Pol II) has evolved an array of heptad repeats with the consensus sequence Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7 at the carboxy-terminal domain (CTD) of the large subunit (Rpb1). Differential phosphorylation of Ser2, Ser5, and Ser7 in the 5M-bM-^@M-^Y and 3M-bM-^@M-^Y regions of genes coordinates the binding of transcription and RNA processing factors to the initiating and elongating polymerase complexes. Here, we report phosphorylation of Thr4 by Polo-like-kinase-3 in mammalian cells. ChIPseq analyses indicate an increase of Thr4-P levels in the 3M-bM-^@M-^Y region of genes occurring subsequently to an increase of Ser2-P levels. A Thr4/Ala mutant of Pol II displays a lethal phenotype. This mutant reveals a global defect in RNA elongation, while initiation is largely unaffected. Since Thr4 replacement mutants are viable in yeast we conclude that this amino acid has evolved an essential function(s) in the CTD of Pol II for gene transcription in mammalian cells. In this study, we investigated the function and ChIPseq genome-wide profiling of Thr4P residue (using the 6D7 antibody) of the Pol II CTD in Raji human B cells in comparison with either total Pol II profiling (N20 antibody, santa-cruz sc-899x), Ser5P CTD (3E8) or Ser2P (3E10) profiling in WT Raji cells. In another set of experiments, we also analysed total Pol II profiling (using an HA tag at the N-terminus of RPB1 and HA antibody Abcam ab9110) when endogenous enzyme is shut down by alpha-amanitin and replaced by either a recominant Pol II with 48 consensus repeats of the CTD (con48) or a mutated version where Thr4 residues were replaced by Ala (Thr4-Ala).In total 6 experimental sets (Pol IIt, Ser5P, Ser2P, Thr4P, con48, Thr4-Ala) were generated for our analysis and for each a biological replicate was performed. Biological replicates were merged when the data showed comparable signal noise ratio. Otherwise a unique replicate, showing the best noise ratio, was chosen for further analysis although the second replicate (for Ser2P and Thr4-Ala experiments). An input control (genomic DNA extracted after reverse crosslinking of the nuclear chip extracts) was performred and used for substraction to the ChIP experiments. One specific input material was used for wt cells, one for con48 and one for Thr4-Ala. Our data were processed to generate final wig files using our in house analysis pipeline essentially as described in Koch et al, (2011) NSMB 18 (8) p956.In brief, after alignment, sequence tags are: (i) artefact removed, (ii) elongated to an in silico optimized actual size of the initial fragments , (iii) input substracted, (iv) merged if applicable, (v) scaled for all experiments to correct for variation of tag number in between experiments. Several of the raw data files were no longer available.

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MudPIT analysis of proteins interacting with Saccharomyces cerevisiae RNA Polymerase II HA-Rpb1 C-Terminal Domain

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