Involved in the export of cellular mRNA to the cytoplasm (PubMed:23149939). Plays a role in the nuclear retention of unspliced mRNAs (PubMed:23149939). Not localized at the nuclear rim. The RNA-binding domain is a non-canonical RNP-type domain. RNAi-mediated knockdown results in severe growth retardation, lethality and reduces the accumulation of unspliced tra-2 in the cytoplasm of rnp-4/RBM8A RNAi mutants. Belongs to the NXF family.