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. Acts as a key regulator of m6A methylation by promoting m6A methylation of mRNAs in the 3'-UTR near the stop codon: recruits the catalytic core components METTL3 and METTL14, thereby guiding m6A methylation at specific sites. Required for mRNA polyadenylation via its role in selective m6A methylation: m6A methylation of mRNAs in the 3'-UTR near the stop codon correlating with alternative polyadenylation (APA). 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 WTAP (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 NUDT21 and CPSF6 (By similarity). 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). Belongs to the vir family.