RNA-binding protein that acts as a key regulator of N6-methyladenosine (m6A) methylation of RNAs, thereby regulating different processes, such as alternative splicing of mRNAs and X chromosome inactivation mediated by Xist RNA (PubMed:16129689, PubMed:27602518). 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:27602518). Plays a key role in m6A methylation, possibly by binding target RNAs and recruiting the WMM complex (PubMed:27602518). Involved in random X inactivation mediated by Xist RNA: acts by binding Xist RNA and recruiting the WMM complex, which mediates m6A methylation, leading to target YTHDC1 reader on Xist RNA and promoting transcription repression activity of Xist (PubMed:27602518). Functions in the regulation of alternative or illicit splicing, possibly by regulating m6A methylation (PubMed:16129689). Inhibits pre-mRNA splicing (PubMed:21044963). Also functions as a mRNA export factor by acting as a cofactor for the nuclear export receptor NXF1 (PubMed:19586903). Component of the WMM complex, a N6-methyltransferase complex composed of a catalytic subcomplex, named MAC, and of an associated subcomplex, named MACOM (PubMed:27602518). The MAC subcomplex is composed of METTL3 and METTL14 (PubMed:27602518). The MACOM subcomplex is composed of WTAP, ZC3H13, CBLL1/HAKAI, VIRMA, and, in some cases of RBM15 (RBM15 or RBM15B) (PubMed:27602518). May interact with NCOR2 (PubMed:16129689). Interacts with NXF1, the interaction is required to promote mRNA export (PubMed:19586903). (Microbial infection) Interacts (via the SPOC domain) with Epstein-Barr virus BMLF1 (via the N-terminus); the interaction is direct. Colocalizes with BMLF1 in the nucleus. Localized in the nucleoplasm with a granular staining pattern and excluded from the nucleoli. Ubiquitously expressed. Belongs to the RRM Spen family. Contaminating sequence. Sequence of unknown origin in the C-terminal part.