Model of Prp19C/NTC function in transcription elongation, nuclear mRNP assembly, and export. Prp19C/NTC (green) consists of the four essential proteins Prp19, Cef1, Syf1, and Clf1 (underlined) and the four nonessential proteins Snt309, Syf2, Isy1, and Ntc20. Isy1, Ntc20, Syf1, and Syf2 (light green) form a subcomplex of Prp19C/NTC. In addition, the essential protein Prp46 and the nonessential protein Cwc15 associate with Prp19C/NTC. Prp19C/NTC is present at transcribed genes through multiple interactions: It interacts directly with RNAPII (gray) via the C-terminal domain of its subunit Syf1. Moreover, the Prp19C/NTC subunits Snt309 and Cef1 interact with Mud2 (blue), which in turn directly binds to the S2-phosphorylated CTD of RNAPII (S2P). Prp19C/NTC facilitates efficient transcription elongation, most likely by its function in the occupancy of TREX (light orange), with which it interacts via its subunits Cwc15 and Syf2. Importantly, Cwc15 also mediates the interaction of Prp19C/NTC with RNAPII and is needed for Prp19C/NTC and TREX occupancy as well as efficient transcription elongation. Furthermore, THO (orange), a subcomplex of TREX, interacts directly with the CTD of RNAPII. Hpr1 (orange) is a THO subunit. TREX also binds to the nascent mRNA (red) and functions in mRNP assembly and nuclear mRNA export.
