Associated component of the WMM complex, a complex that mediates N6-methyladenosine (m6A) methylation of RNAs, a modification that plays a role in the efficiency of mRNA splicing and RNA processing (PubMed:29535189, PubMed:29547716). Acts as a key regulator of m6A methylation by promoting m6A methylation of mRNAs at the 3'-UTR (PubMed:29547716). Required for accumulation of METTL3 and METTL14 to nuclear speckle (By similarity). Acts as a mRNA splicing regulator (By similarity). Regulates G2/M cell-cycle transition by binding to the 3' UTR of CCNA2, which enhances its stability (By similarity). Impairs WT1 DNA-binding ability and inhibits expression of WT1 target genes (By similarity). Component of the WMM complex, a N6-methyltransferase complex composed of a catalytic subcomplex, named MAC, and of an associated subcomplex, named MACOM (PubMed:29535189, PubMed:29547716). The MAC subcomplex is composed of METTL3 and METTL14 (PubMed:29535189, PubMed:29547716). The MACOM subcomplex is composed of WTAP, ZC3H13, CBLL1/HAKAI, VIRMA, and, in some cases of RBM15 (RBM15 or RBM15B) (PubMed:29535189, PubMed:29547716). Interacts with WT1 (By similarity). Also a component of a MACOM-like complex, named WTAP complex, composed of WTAP, ZC3H13, CBLL1, VIRMA, RBM15, BCLAF1 and THRAP3 (By similarity). Interacts with CPNE4 (via VWFA domain) (PubMed:12522145). Mainly nuclear with some fraction located in the cytoplasm (PubMed:29547716). ZC3H13 is required to anchor component of the MACOM subcomplex, such as VIRMA, in the nucleus (PubMed:29547716). Death at E6.5 due to defecs in cell proliferation. Belongs to the fl(2)d family.