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. 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. Plays a key role in m6A methylation, possibly by binding target RNAs and recruiting the WMM complex. 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. Functions in the regulation of alternative or illicit splicing, possibly by regulating m6A methylation. Inhibits pre-mRNA splicing. Also functions as a mRNA export factor by acting as a cofactor for the nuclear export receptor NXF1. Component of the WMM complex, a N6-methyltransferase complex composed of a catalytic subcomplex, named MAC, and of an associated subcomplex, named MACOM. 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). May interact with NCOR2. Interacts with NXF1, the interaction is required to promote mRNA export. Colocalizes with BMLF1 in the nucleus. Localized in the nucleoplasm with a granular staining pattern and excluded from the nucleoli. Belongs to the RRM Spen family. Aberrant splicing.