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:24981863, PubMed:29507755). 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 (PubMed:29507755). 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) (PubMed:29507755). Component of the WMM complex, a N6-methyltransferase complex composed of a catalytic subcomplex, named MAC, and of an associated subcomplex, named MACOM (PubMed:29507755). The MAC subcomplex is composed of METTL3 and METTL14. The MACOM subcomplex is composed of WTAP, ZC3H13, CBLL1/HAKAI, VIRMA, and, in some cases of RBM15 (RBM15 or RBM15B) (PubMed:24981863, PubMed:29507755). Interacts with WTAP (PubMed:24100041). Also a component of a MACOM-like complex, named WTAP complex, composed of WTAP, ZC3H13, CBLL1, VIRMA, RBM15, BCLAF1 and THRAP3 (PubMed:24100041). Interacts with NUDT21 and CPSF6 (PubMed:29507755). Mainly nuclear with some fraction located in the cytoplasm. ZC3H13 is required to anchor component of the MACOM subcomplex, such as VIRMA, in the nucleus. Belongs to the vir family.