Physical and functional association of RNA polymerase II and the proteasome

Abstract

Recent studies from a number of laboratories have revealed a surprising number of connections between RNA polymerase II transcription and the ubiquitin͞proteasome pathway. We now find yet another intersection of these pathways by showing that the 26S proteasome associates with regions of the GAL1, GAL10, and HSP82 genes, including the 3 ends, in a transcription-dependent fashion. The appearance of the proteasome on these inducible genes correlates with both the accumulation of transcripts and the buildup of RNA polymerase II complexes in the same region. Furthermore, the 26S proteasome and RNA polymerase II coimmunoprecipitate, and inhibition of 26S proteolytic activity leads to increased read through of a transcription termination site. We suggest that the proteasome is generally recruited to the DNA at sites of stalled RNA polymerase and may act to resolve these complexes. Recent research has demonstrated several connections between the 26S proteasome, or its subunits, and RNA polymerase II (pol II) transcription. We demonstrated that several proteins from the 19S regulatory particle, but not the 20S proteolytic unit (1), of the 26S proteasome (2) associate directly with the yeast Gal4 activator and are recruited to activated GAL promoters (3). The 19S has also been shown to be critical for efficient elongation by RNA pol II in both yeast and mammalian cells, and this activity does not require the proteolytic activity of the proteasome (4, 5). In addition to this role in elongation, we have also found that this proteasome subcomplex, which we have termed APIS (3), negatively regulates Gal4-promoter interactions in vivo, again in a nonproteolytic fashion (A.D., F.G., A. Ferdous, T.K., and S.A.J., unpublished observations). In contrast to the evidence for nonproteolytic activities of the proteasome in transcription, several laboratories noted an inverse correlation between the potency of many transcriptional activators and the protein level in the cell (6-9), suggesting an intimate mechanistic link between the process of transcriptional activation and the turnover of the activator via the ubiquitinproteasome pathway. This idea has been further supported by the recent finding that proteasome inhibitors strongly inhibit estrogen receptor-mediated transcription and specifically block cycling of the estrogen receptor and other transcription factors on and off estrogen-responsive promoters (10). These results suggest that the 20S as well as the 19S subunit might be directly involved in the transcriptional process. Here, we examine this possibility and report another intersection between the transcription and ubiquitin-proteasome pathways.In our previous study of the recruitment of the APIS complex to the GAL1͞10 promoter, we showed that promoter DNA was coprecipitated with antibodies raised against several of the proteasomal ATPases in a chromatin immunoprecipitation (ChIP) assay, but that little or no promoter DNA was brought down by using antibodies raised against the 20S core subunit of the proteasome or proteins ...

Identifying Dynamic Interactors of Protein Complexes by Quantitative Mass Spectrometry

“…UBLCP1 has been shown to dephosphorylate the CTD of RNA polymerase II in vitro (40). In addition, recent studies have physically and functionally linked the 26 S proteasome with RNA polymerase II in vivo (41). Together with the findings reported here, these results raise the possibility that UBLCP1 may be a shuttling factor that links the proteasome complex to transcriptional control.…”

A Ubiquitin-Proteasome Pathway for the Repair of Topoisomerase I-DNA Covalent Complexes

“…The requirement for transcription for the assembly of the polyubiquitin chains on Top1 is interesting. Previous studies have suggested that proteasome components are associated with RNA polymerase II and are required for efficient transcription elongation (37,38). It is possible that the collision between the Top1 cleavage complex and the elongating RNA polymerase may bring the proteasome components into close proximity of the colliding complexes and facilitate proteasomal degradation of Top1.…”

Cytoskeleton-Associated Large RNP Complexes in Tobacco Male Gametophyte (EPPs) Are Associated with Ribosomes and Are Involved in Protein Synthesis, Processing, and Localization

“…[51][52][53] Moreover, a number of transcripts encoding proteasome-associated and F-box proteins were identified in Arabidopsis developing and germinating pollen. 42,54 Proteasomes were also demonstrated to perform other nonproteolytic functions including transcriptional regulation, [55][56][57] RNase activity, 58,59 translational regulation, 60,61 and possessing cytoskeleton-binding properties. 52,62 With regard to all abovementioned alternative functions, the presence of proteasome subunits within EPP complexes is natural in relation to complex EPP-associated spatially and temporarily regulated activities.…”