The function of ENSG00000131051 (RBM39, RNA binding motif protein 39) is as follows. RNA-binding protein that acts as a pre-mRNA splicing factor (PubMed:15694343, PubMed:24795046, PubMed:28302793, PubMed:28437394, PubMed:31271494). Acts by promoting exon inclusion via regulation of exon cassette splicing (PubMed:31271494). Also acts as a transcriptional coactivator for steroid nuclear receptors ESR1/ER-alpha and ESR2/ER-beta, and JUN/AP-1, independently of the pre-mRNA splicing factor activity (By similarity). {ECO:0000250|UniProtKB:Q8VH51, ECO:0000269|PubMed:15694343, ECO:0000269|PubMed:24795046, ECO:0000269|PubMed:28302793, ECO:0000269|PubMed:28437394, ECO:0000269|PubMed:31271494}.