4c31
From Proteopedia
Nup1:Sac3:Sus1 complex
Structural highlights
Function[SAC3_YEAST] Component of the SAC3-THP1 complex, which functions in transcription-coupled mRNA export from the nucleus to the cytoplasm. SAC3-THP1 functions in docking export-competent ribonucleoprotein particles (mRNPs) to the nuclear entrance of the nuclear pore complex (nuclear basket), by association with components of the nuclear mRNA export machinery (MEX67-MTR2 and SUB2) in the nucleoplasm and the nucleoporin NUP1 at the nuclear basket.[1] [2] [NUP1_YEAST] Functions as a component of the nuclear pore complex (NPC). NPC components, collectively referred to as nucleoporins (NUPs), can play the role of both NPC structural components and of docking or interaction partners for transiently associated nuclear transport factors. Active directional transport is assured by both, a Phe-Gly (FG) repeat affinity gradient for these transport factors across the NPC and a transport cofactor concentration gradient across the nuclear envelope (GSP1 and GSP2 GTPases associated predominantly with GTP in the nucleus, with GDP in the cytoplasm). As one of the FG repeat nucleoporins NUP1 is involved in interactions with and guidance of nuclear transport receptors such as SRP1-KAP95 (importin alpha and beta) through the NPC. Like the closely related NUP2 it also plays an important role in disassembling and recycling SRP1-KAP95 to the cytoplasm after nuclear import. Upon entry of the heterotrimeric SRP1-KAP95-cargo complex in the nucleus, NUP1 binds through its C-terminus to KAP95, thus accelerating the release of KAP95 and, indirectly, of the nuclear localization signal (NLS)-containing cargo from the SRP1-KAP95-cargo complex.[3] [4] [5] [6] [7] [8] [9] [10] [11] [SUS1_YEAST] Involved in mRNA export coupled transcription activation by association with both the TREX-2 and the SAGA complexes. The transcription regulatory histone acetylation (HAT) complex SAGA is involved in RNA polymerase II-dependent regulation of approximately 10% of yeast genes. At the promoters, SAGA is required for recruitment of the basal transcription machinery. It influences RNA polymerase II transcriptional activity through different activities such as TBP interaction (SPT3, SPT8 and SPT20) and promoter selectivity, interaction with transcription activators (GCN5, ADA2, ADA3 and TRA1), and chromatin modification through histone acetylation (GCN5) and deubiquitination (UBP8). SUS1 forms a distinct functional SAGA module with UBP8, SGF11 and SGF73 required for deubiquitination of H2B and for the maintenance of steady-state H3 methylation levels. The TREX-2 complex functions in docking export-competent ribonucleoprotein particles (mRNPs) to the nuclear entrance of the nuclear pore complex (nuclear basket), by association with components of the nuclear mRNA export machinery (MEX67-MTR2 and SUB2) in the nucleoplasm and the nucleoporin NUP1 at the nuclear basket. TREX-2 participates in mRNA export and accurate chromatin positioning in the nucleus by tethering genes to the nuclear periphery. SUS1 has also a role in mRNP biogenesis and maintenance of genome integrity through preventing RNA-mediated genome instability. Finally SUS1 has a role in response to DNA damage induced by methyl methane sulfonate (MMS) and replication arrest induced by hydroxyurea.[12] [13] [14] [15] [16] [17] [18] Publication Abstract from PubMedThe conserved Sac3:Thp1:Sem1:Sus1:Cdc31 (TREX2) complex binds to nuclear pore complexes (NPCs) and, in addition to integrating mRNA nuclear export with preceding steps in the gene expression pathway, facilitates re-positioning of highly regulated actively transcribing genes (such as GAL1) to NPCs. Although TREX2 is thought to bind NPC protein Nup1, defining the precise role of this interaction has been frustrated by the complex pleiotropic phenotype exhibited by nup1Delta strains. To provide a structural framework for understanding the binding of TREX2 to NPCs and its function in the gene expression pathway, we have determined the structure of the Nup1:TREX2 interaction interface and used this information to engineer a Sac3 variant that impairs NPC binding while not compromising TREX2 assembly. This variant inhibited the NPC association of both de-repressed and activated GAL1 and also produced mRNA export and growth defects. These results indicate that the TREX2:Nup1 interaction facilitates the efficient nuclear export of bulk mRNA together with the re-positioning of GAL1 to NPCs that is required for transcriptional control that is mediated by removal of SUMO from repressors by NPC-bound Ulp1. Structural basis for binding the TREX2 complex to nuclear pores, GAL1 localisation and mRNA export.,Jani D, Valkov E, Stewart M Nucleic Acids Res. 2014 Apr 4. PMID:24705649[19] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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