Regulatory component of the SET1 complex implicated in the tethering of this complex to transcriptional start sites of active genes (By similarity). 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) (By similarity). 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 (By similarity). 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: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 (By similarity). Component of the PTW/PP1 phosphatase complex, composed of PPP1R10/PNUTS, TOX4, WDR82, and PPP1CA or PPP1CB or PPP1CC (By similarity). Associated with multiple protein complexes including an RNA polymerase II complex, MLL3/MLL4 complex and a chaperonin-containing TCP1 complex (By similarity). Interacts with CUL4B (PubMed:17041588). Interacts with RBBP5 and SETD1B (By similarity). Interacts with SETD1A (via RRM domain) (By similarity). Interacts with POLR2B (By similarity). Interacts with hyperphosphorylated C-terminal domain (CTD) of RNA polymerase II large subunit (POLR2A) (By similarity). Binds specifically to CTD heptad repeats phosphorylated on 'Ser-5' of each heptad (By similarity). SETD1A enhances its interaction with POLR2A (By similarity). Interacts with PPP1R10/PNUTS (By similarity). Interacts with PPP1CA in the presence of PPP1R10/PNUTS (By similarity). Interacts with ZC3H4; interaction is independent of the SET1 complex and promotes transcription termination of long non-coding RNAs (lncRNAs) (PubMed:33767452). Associates with chromatin (By similarity). Recruited at sites of high RNA polymerase II occupancy (PubMed:33767452). Belongs to the WD repeat SWD2 family.