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). Controls embryonic stem cells (ESCs) pluripotency via its role in m6A methylation (PubMed:29547716). In the WMM complex, anchors component of the MACOM subcomplex in the nucleus (PubMed:29547716). Also required for bridging WTAP to the RNA-binding component RBM15 (RBM15 or RBM15B) (PubMed:29535189). 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). Also a component of a MACOM-like complex, named WTAP complex, composed of WTAP, ZC3H13, CBLL1/HAKAI, VIRMA, RBM15, BCLAF1 and THRAP3 (By similarity). Belongs to the ZC3H13 family.