Regulatory component of the SET1 complex implicated in the tethering of this complex to transcriptional start sites of active genes (PubMed:17998332, PubMed:18838538, PubMed:20516061). Facilitates histone H3 'Lys-4' methylation (H3K4me) via recruitment of the SETD1A or SETD1B to the 'Ser-5' phosphorylated C-terminal domain (CTD) of RNA polymerase II large subunit (POLR2A) (PubMed:17998332, PubMed:18838538). Component of PTW/PP1 phosphatase complex, which plays a role in the control of chromatin structure and cell cycle progression during the transition from mitosis into interphase (PubMed:20516061). Together with ZC3H4, but independently of the SET1 complex, part of a transcription termination checkpoint that promotes transcription termination of long non-coding RNAs (lncRNAs) (PubMed:33913806, PubMed:33767452). The transcription termination checkpoint is activated by the inefficiently spliced first exon of lncRNAs and promotes transcription termination of lncRNAs and their subsequent degradation by the exosome (PubMed:33767452). Component of the SET1 complex, at least composed of the catalytic subunit (SETD1A or SETD1B), WDR5, WDR82, RBBP5, ASH2L/ASH2, CXXC1/CFP1, HCFC1 and DPY30 (PubMed:16253997, PubMed:17355966, PubMed:17998332, PubMed:18838538). Component of the PTW/PP1 phosphatase complex, composed of PPP1R10/PNUTS, TOX4, WDR82, and PPP1CA or PPP1CB or PPP1CC (PubMed:20516061). Associated with multiple protein complexes including an RNA polymerase II complex, MLL3/MLL4 complex and a chaperonin-containing TCP1 complex (PubMed:20516061). Interacts with CUL4B (PubMed:17041588). Interacts with RBBP5 and SETD1B (PubMed:17998332, PubMed:18838538). Interacts with SETD1A (via RRM domain) (PubMed:17998332). Interacts with POLR2B (PubMed:17998332). Interacts with hyperphosphorylated C-terminal domain (CTD) of RNA polymerase II large subunit (POLR2A) (PubMed:17998332). Binds specifically to CTD heptad repeats phosphorylated on 'Ser-5' of each heptad (PubMed:17998332). SETD1A enhances its interaction with POLR2A (PubMed:17998332). Interacts with PPP1R10/PNUTS (PubMed:20516061). Interacts with PPP1CA in the presence of PPP1R10/PNUTS (PubMed:20516061). Interacts with ZC3H4; interaction is independent of the SET1 complex and promotes transcription termination of long non-coding RNAs (lncRNAs) (PubMed:33913806). Associates with chromatin (PubMed:20516061). Recruited at sites of high RNA polymerase II occupancy (By similarity). Belongs to the WD repeat SWD2 family. The gene encoding this protein shares one overlapping exon with TMEM113. Truncated N-terminus.