[Isoform A]: RNA binding protein that mediates the regulation of pre-mRNA alternative splicing (AS) (PubMed:24860013, PubMed:26347403). Acts either as activator (FLNB, HSPG2, LIPA1, MYOCD, PTPRF and PPFIBP1) or repressor (TPM1, ACTN1, ITGA7, PIEZO1, LSM14B, MBNL1 and MBML2) of splicing events on specific pre-mRNA targets (By similarity). Together with RNA binding proteins RBFOX2 and MBNL1/2, activates a splicing program associated with differentiated contractile vascular smooth muscle cells (SMC) by regulating AS of numerous pre- mRNA involved in actin cytoskeleton and focal adhesion machineries, suggesting a role in promoting a cell differentiated state (By similarity). Binds to introns, exons and 3'-UTR associated with tandem CAC trinucleotide motifs separated by a variable spacer region, at a minimum as a dimer. The minimal length of RNA required for RBPMS- binding tandem CAC motifs is 15 nt, with spacing ranging from 1 to 9 nt. Can also bind to CA dinucleotide repeats (PubMed:24860013, PubMed:26347403). Mediates repression of TPM1 exon 3 by binding to CAC tandem repeats in the flanking intronic regions, followed by higher- order oligomerization and heterotypic interactions with other splicing regulators including MBNL1 and RBFOX2, which prevents assembly of ATP- dependent splicing complexes (By similarity). {ECO:0000250|UniProtKB:A0A8I6G705, ECO:0000269|PubMed:24860013, ECO:0000269|PubMed:26347403}. [Isoform C]: Acts as a regulator of pre-mRNA alternative splicing (AS) (By similarity). Binds mRNA (PubMed:17099224). Regulates AS of ACTN1, FLNB, although with lower efficiency than isoform A / RBPMSA (By similarity). Acts as coactivator of SMAD transcriptional activity in a TGFB1-dependent manner, possibly through increased phosphorylation of SMAD2 and SMAD3 at the C-terminal SSXS regions and promotion of the nuclear accumulation of SMAD proteins (PubMed:17099224). {ECO:0000250|UniProtKB:A0A8I6G705, ECO:0000269|PubMed:17099224}. This is the function of RBPMS (RNA binding protein, mRNA processing factor, ENSG00000157110).