Figure 7.

The Sac3 PCI Domain Promotes Transcription and mRNA Export

Mechanism for a relay between TREX-2, Mediator, and Pol II. Model depicts the putative overall topology of TREX-2 and its interaction with Mediator. (1) Docking to Mediator involves the conserved pair of Sac3 R256/R288 residues (red sticks) and the Med31 submodule (magenta). (2) TREX-2 regulates Cdk8 kinase module association. (3) TREX-2, Cdk8, and Med31 impact on RNA Pol II CTD Ser5 phosphorylation (S5; yellow). (4) TREX-2 also influences mRNA export via the PCI surface centered around the Sac3 R256/R288 residues. Other mRNA adaptor/export proteins are depicted as circles. Transition between Pol II initiation and early elongation is shown. TREX-2 attaches to the NPC basket through an NPC anchor domain comprising a 12.5 nm long Sac3 helix, two Sus1 molecules and Cdc31 (all in gray, PDB: 3fwc).