Sus1 is recruited to coding regions and functions during transcription elongation in association with SAGA and TREX2

Abstract

Gene transcription, RNA biogenesis, and mRNA transport constitute a complicated process essential for all eukaryotic cells. The transcription/export factor Sus1 plays a key role in coupling transcription activation with mRNA export, and it resides in both the SAGA and TREX2 complexes. Moreover, Sus1 is responsible for GAL1 gene gating at the nuclear periphery, which is important for its transcriptional status. Here, we show that Sus1 is required during transcription elongation and is associated with the elongating form of RNA Polymerase II (RNAP II) phosphorylated on Ser5 and Ser2 of the C-terminal domain (CTD). In addition, Sus1 copurifies with the essential mRNA export factors Yra1 and Mex67, which bind to the mRNA cotranscriptionally. Consistently, ChIP analysis reveals that Sus1 is present at coding regions dependent on transcription in a manner stimulated by Kin28-dependent CTD phosphorylation. Strikingly, eliminating the TREX2 component Sac3 or the SAGA subunit Ubp8 partially impairs Sus1 targeting to coding sequences and upstream activating sequences (UAS). We found, unexpectedly, that Sgf73 is necessary for association of Sus1 with both SAGA and TREX2, and that its absence dramatically reduces Sus1 occupancy of UAS and ORF sequences. Our results reveal that Sus1 plays a key role in coordinating gene transcription and mRNA export by working at the interface between the SAGA and TREX2 complexes during transcription elongation.[Keywords: Sus1; SAGA; TREX2; transcription elongation; mRNA export] Supplemental material is available at http://www.genesdev.org.

Connecting the transcription site to the nuclear pore: a multi-tether process that regulates gene expression

“…Together with gene localization experiments, these observations indicate that SAGA and TREX2 act synergistically to recruit Sus1 to chromatin, and to promote gene-NPC anchoring (Jani et al, 2009;Kohler et al, 2006;Pascual-Garcia et al, 2008). In light of these findings and because of the earlier observation that the interaction of Nup2 with GAL gene promoters does not require SAGA components (Schmid et al, 2006), it is conceivable that gene repositioning to the NPC occurs mainly in two steps: the interaction of specific promoter-bound transcription activators with nucleoporins mediates the initial binding to the NPC, whereas the subsequent recruitment of SAGA might stabilize gene-NPC anchoring by interacting with TREX2 at a minimum.…”

“…Reinforcing the view that transcription elongation events contribute to gene-NPC gating, it was reported that the export factor Sus1 is loaded on the elongating machinery through interaction with the phosphorylated CTD of RNA Pol II, and that it functions with SAGA and TREX2 not only during transcription initiation but also during elongation (Faza et al, 2009;GonzalezAguilera et al, 2008;Govind et al, 2007;Pascual-Garcia et al, 2008;Wyce et al, 2007). Notably, TREX2 mutants exhibit defects in transcription elongation as well as enhanced transcriptiondependent hyper-recombination.…”

Nuclear export of mRNA and its regulation by ubiquitylation

“…Intriguingly, recent studies in yeast have also implicated the coupling of transcriptional initiation machinery with mRNA export. 15,[58][59][60] In these studies, Sus1 has been identified to link the co-activator SAGA complex with the TREX-2 complex (which consists of the subunits Sac3, Thp1, Cdc31 and Sus1). TREX-2 interacts with NPC via nucleoporins, Nup1 and Nup60.…”

Vps Factors Are Required for Efficient Transcription Elongation in Budding Yeast

“…Importantly, as observed for conventional elongation factors, the association of Vps proteins with ARG1 or GAL1 CDS was strongly dependent on target gene transcription, occurring at high levels only under conditions where the relevant transcriptional activators are induced (Gcn4) or functional (Gal4). In addition, the TATA promoter element is required for high-level Vps15 and Vps34 occupancies at ARG1 under inducing conditions, and Vps15 and Vps34 occupancies of ARG1 CDS were stimulated by the Pol II CTD kinase Cdk7/ Kin28-a characteristic of numerous factors involved in cotranscriptional histone modifications, mRNA processing or nuclear export, and the elongation or termination phases of transcription (Phatnani and Greenleaf 2006;Govind et al 2007;Pascual-Garcia et al 2008;Ginsburg et al 2009;Govind et al 2010;Qiu et al 2012).…”