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The THP1-SAC3-SUS1-CDC31 complex works in transcription elongation-mRNA export preventing RNA-mediated genome instability

Centro Andaluz de Biologia Molecular y Medicina Regenerativa, Universidad de Sevilla-CSIC, 41092 Sevilla, Spain.
Molecular biology of the cell (Impact Factor: 5.98). 08/2008; 19(10):4310-8. DOI: 10.1091/mbc.E08-04-0355
Source: PubMed

ABSTRACT The eukaryotic THO/TREX complex, involved in mRNP biogenesis, plays a key role in the maintenance of genome integrity in yeast. mRNA export factors such as Thp1-Sac3 also affect genome integrity, but their mutations have other phenotypes different from those of THO/TREX. Sus1 is a novel component of SAGA transcription factor that also associates with Thp1-Sac3, but little is known about its effect on genome instability and transcription. Here we show that Thp1, Sac3, and Sus1 form a functional unit with a role in mRNP biogenesis and maintenance of genome integrity that is independent of SAGA. Importantly, the effects of ribozyme-containing transcription units, RNase H, and the action of human activation-induced cytidine deaminase on transcription and genome instability are consistent with the possibility that R-loops are formed in Thp1-Sac3-Sus1-Cdc31 as in THO mutants. Our data reveal that Thp1-Sac3-Sus1-Cdc31, together with THO/TREX, define a specific pathway connecting transcription elongation with export via an RNA-dependent dynamic process that provides a feedback mechanism for the control of transcription and the preservation of genetic integrity of transcribed DNA regions.

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    • "The N-terminal RRM, LRR, and NTF2L domains are thought to recognize RNA, whereas the NTF2L domain binds Mtr2 and, together with the UBA domain, provides lowaffinity binding sites for nucleoporin FG repeats (Kang et al., 1999; Liker et al., 2000; Fribourg et al., 2001; Bachi et al., 2000; Grant et al., 2002, 2003; Aibara et al., 2015). Transcription export complex 2 (TREX-2) contributes to both mRNA nuclear export and its integration with the nuclear steps of the gene expression pathway (Rodriguez-Navarro et al., 2004; Gonzá lez-Aguilera et al., 2008). TREX-2 is based on a Sac3 scaffold (Figure 1A) to which Thp1, Sem1, Sus1, and Cdc31 bind, and is localized primarily at NPCs through interactions with proteins located on the nucleoplasmic face, including Nup1 (Fischer et al., 2002, 2004; Faza et al., 2009; Jani et al., 2009, 2014; Ellisdon and Stewart, 2012). "
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    ABSTRACT: The TREX-2 complex integrates mRNA nuclear export into the gene expression pathway and is based on a Sac3 scaffold to which Thp1, Sem1, Sus1, and Cdc31 bind. TREX-2 also binds the mRNA nuclear export factor, Mex67:Mtr2, through the Sac3 N-terminal region (Sac3N). Here, we characterize Chaetomium thermophilum TREX-2, show that the in vitro reconstituted complex has an annular structure, and define the structural basis for interactions between Sac3, Sus1, Cdc31, and Mex67:Mtr2. Crystal structures show that the binding of C. thermophilum Sac3N to the Mex67 NTF2-like domain (Mex67(NTF2L)) is mediated primarily through phenylalanine residues present in a series of repeating sequence motifs that resemble those seen in many nucleoporins, and Mlp1 also binds Mex67:Mtr2 using a similar motif. Deletion of Sac3N generated growth and mRNA export defects in Saccharomyces cerevisiae, and we propose TREX-2 and Mlp1 function to facilitate export by concentrating mature messenger ribonucleoparticles at the nuclear pore entrance. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.
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    • "However, its role in transcription elongation is independent of SAGA and is linked to mRNA export. It has been proposed that a feedback mechanism exists by which improperly formed mRNPs, presumably stacked at the nuclear pore, have a backward effect promoting transcription impairment and genetic instability (González-Aguilera et al., 2008). "
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    • "Several authors, including ourselves , have proposed a role for Sus1 during transcription elongation. Gonzalez-Aguilera and coworkers showed that transcription elongation is impaired in sus1Δ mutants in vivo, but only slightly in vitro, and they concluded that sus1Δ leads to similar gene expression defects as those of mutants thp1Δ and sac3Δ [71]. "
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