Abstract
Bud27, the yeast orthologue of human URI/RMP, is a member of the prefoldin-like family of ATP-independent molecular chaperones. It has recently been shown to mediate the assembly of the three RNA polymerases in an Rpb5-dependent manner. In this work, we present evidence of Bud27 modulating RNA pol II transcription elongation. We show that Bud27 associates with RNA pol II phosphorylated forms (CTD-Ser5P and CTD-Ser2P), and that its absence affects RNA pol II occupancy of transcribed genes. We also reveal that Bud27 associates in vivo with the Sth1 component of the chromatin remodeling complex RSC and mediates its association with RNA pol II. Our data suggest that Bud27, in addition of contributing to Rpb5 folding within the RNA polymerases, also participates in the correct assembly of other chromatin-associated protein complexes, such as RSC, thereby modulating their activity.
Highlights
The unconventional prefoldin Rpb5 interactor (URI/RMP), and its orthologue in yeast, Bud27, are members of the prefoldin (PFD) family of adenosine triphosphate (ATP)-independent molecular chaperones [1,2,3,4]
All the rpb5 point mutations affecting growth of the bud27Δ strain lie at the C-terminal globe of Rpb5. This motif, which is conserved from archaea to higher eukaryotes, is involved in the interaction of Rpb5 with Rpb1, in a region directly associated with the RNA polymerases (RNA pol) II cleft domain (␣45–47 of Rpb1)
It bears noting that these genetic interactions reflect the participation of both proteins in common biological process and seems not to be the consequence of a loss of physical contact between Rpb5 and Bud27, as we demonstrated by two-hybrid analyses (Supplementary Figure S1)
Summary
The unconventional prefoldin Rpb interactor (URI/RMP), and its orthologue in yeast, Bud, are members of the prefoldin (PFD) family of adenosine triphosphate (ATP)-independent molecular chaperones [1,2,3,4]. URI was originally identified as a protein binding the Rpb subunit of all three nuclear RNA polymerases (RNA pol) [5] and is considered to function as a scaffold protein able to assemble additional members of the PFD family in both human and yeast [2,3,6]. URI has been linked to essential cellular processes, such as translation initiation [8], genome stability and DNA damage response, and it is required for viability in Drosophila, Caenorhabditis and human cells [2,9,10]. Both URI and Bud have been reported to be involved in transcription. A role for human URI as a transcriptional co-repressor has been proposed, through its interaction with the general transcription factor TFIIF, which binds Rpb, and with the hepatitis virus X protein (HBx) [5,11,12]
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