The Nuclear Pore-Associated TREX-2 Complex Employs Mediator to Regulate Gene Expression.
Bottom Line: Transcriptome and phenotypic profiling confirm that TREX-2 and Med31 are functionally interdependent at specific genes.TREX-2 additionally uses its Mediator-interacting surface to regulate mRNA export suggesting a mechanism for coupling transcription initiation and early steps of mRNA processing.Our data provide mechanistic insight into how an NPC-associated adaptor complex accesses the core transcription machinery.
Affiliation: Max F. Perutz Laboratories, Medical University of Vienna, Vienna Biocenter Campus (VBC), Dr. Bohr-Gasse 9/3, 1030 Vienna, Austria.Show MeSH
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Mentions: To find out whether the influence of TREX-2 on Mediator is direct, Mediator was purified from cells expressing N-terminally myc-tagged versions of Sac3 (Figure 3A). Indeed, the TREX-2 core subunit Sac3 could be readily detected in Mediator purifications. Notably, mutation of either Sac3 R256 or R288 resulted in significantly lower amounts of TREX-2 associated with Mediator. This effect was particularly pronounced when the charge of the side-chain was inverted (i.e., R256D and R288D). The sac3 R288D mutant, which displayed the weakest affinity toward Mediator partially recapitulated the deletion of the entire SAC3 gene with respect to Cdk8 disassembly, Pol II dissociation, and increased Ser5 phosphorylation levels. To investigate whether TREX-2 binds Mediator through the CKM, we tested whether deletions of kinase module subunits would impair TREX-2 binding. However, TREX-2 co-purified efficiently with Mediator even when the module was disrupted (Figure 3B). Thus, TREX-2 regulates association of the CKM with Mediator, yet, without using the CKM as a docking site.
Affiliation: Max F. Perutz Laboratories, Medical University of Vienna, Vienna Biocenter Campus (VBC), Dr. Bohr-Gasse 9/3, 1030 Vienna, Austria.