RNA-binding protein that plays a role in the regulation of alternative splicing and influences mRNA splice site selection and exon inclusion. Binds preferentially to the 5'-[AU]UAAA-3' motif in vitro (PubMed:19457263). Binds optimally to RNA containing 5'-[AU]UAA-3' as a bipartite motif spaced by more than 15 nucleotides (By similarity). Binds poly(A). RNA-binding abilities are down-regulated by tyrosine kinase PTK6 (PubMed:15471878). Involved in splice site selection of vascular endothelial growth factor (By similarity). In vitro regulates CD44 alternative splicing by direct binding to purine-rich exonic enhancer (By similarity). 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. High concentrations in forebrain structures block splicing inclusion of NRXN1-3 AS4 exons while low concentrations favor their inclusion. Targeted, cell-type specific splicing regulation of NRXN1 at AS4 is involved in neuronal glutamatergic synapse function and plasticity and is linked to behavioral aspects (PubMed:22196734, PubMed:23637638, PubMed:24469635, PubMed:27174676). Regulates expression of KHDRBS2/SLIM-1 in defined neuron populations in the hippocampus by modifying its alternative splicing resulting in a transcript predicted to undergo nonsense-mediated decay (PubMed:25505328). Can bind FABP9 mRNA (PubMed:19916944). May play a role as a negative regulator of cell growth. Inhibits cell proliferation. Self-associates to form homooligomers; dimerization increases RNA affinity (By similarity). Interacts with KHDRBS2/SLM-1 (By similarity). Interacts with KHDRBS1/SAM68; heterooligomer formation of KHDRBS family proteins may modulate RNA substrate specificity (PubMed:10077576). Interacts with the splicing regulatory proteins SFRS9, SAFB and YTHDC1. Interacts with HNRPL, RBMX, RBMY1A1, p85 subunit of PI3-kinase, SERPINB5 (By similarity). Localized in a compartment adjacent to the nucleolus, but distinct from the peri-nucleolar one. Highly expressed in testis and brain. In adult cerebellum expressed predominantly in internal granular layer interneurons and in hippocampus is exclusively expressed in CA neurons; expression is restricted to neuronal subpopulations largely non-overlapping with expression of KHDRBS2/SLM-1. In the developing cerebellum expression is decreasing in the first 3 postnatal weeks. The proline-rich site binds the SH3 domain of the p85 subunit of PI3-kinase. Phosphorylated on tyrosine residues by PTK6. Belongs to the KHDRBS family.