RNA-binding protein that plays a role in the regulation of alternative splicing and influences mRNA splice site selection and exon inclusion (PubMed:11118435). Binds preferentially to the 5'-[AU]UAAA-3' motif in vitro. Binds optimally to RNA containing 5'-[AU]UAA-3' as a bipartite motif spaced by more than 15 nucleotides. Binds poly(A). RNA-binding abilities are down-regulated by tyrosine kinase PTK6 (By similarity). Involved in splice site selection of vascular endothelial growth factor. In vitro regulates CD44 alternative splicing by direct binding to purine-rich exonic enhancer (PubMed:11118435). Can regulate alternative splicing of neurexins NRXN1-3 in the laminin G-like domain 6 containing the evolutionary conserved neurexin alternative spliced segment 4 (AS4) involved in neurexin selective targeting to postsynaptic partners such as neuroligins and LRRTM family members. Targeted, cell-type specific splicing regulation of NRXN1 at AS4 is involved in neuronal glutamatergic synapse function and plasticity. May regulate expression of KHDRBS2/SLIM-1 in defined brain neuron populations by modifying its alternative splicing. Can bind FABP9 mRNA (By similarity). May play a role as a negative regulator of cell growth. Inhibits cell proliferation (By similarity). Self-associates to form homooligomers; dimerization increases RNA affinity (By similarity). Interacts with KHDRBS1/SAM68 and KHDRBS2/SLM-1; heterooligomer formation of KHDRBS family proteins may modulate RNA substrate specificity (PubMed:15345239). Interacts with the splicing regulatory proteins SFRS9, SAFB and YTHDC1. Interacts with HNRPL (PubMed:11118435). Interacts with RBMX, RBMY1A1, p85 subunit of PI3-kinase, SERPINB5 (By similarity). Ubiquitous. Highly expressed in brain, heart, testis and in Sertoli cells at all stages of spermatogenesis. Expressed in neurons. Detected in cortical layers of the forebrain and in the CA1 to CA4 regions of the hippocampus. The proline-rich site binds the SH3 domain of the p85 subunit of PI3-kinase. Phosphorylated on tyrosine residues. Belongs to the KHDRBS family.