The function of KHDRBS3 (KH RNA binding domain containing, signal transduction associated 3, Ensembl gene identifier ENSG00000131773) is as follows. 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. 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 (PubMed:10564820, PubMed:19561594, PubMed:26758068). Involved in splice site selection of vascular endothelial growth factor (PubMed:15901763). 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 (PubMed:26758068). Targeted, cell-type specific splicing regulation of NRXN1 at AS4 is involved in neuronal glutamatergic synapse function and plasticity (By similarity). May regulate expression of KHDRBS2/SLIM-1 in defined brain neuron populations by modifying its alternative splicing (By similarity). Can bind FABP9 mRNA (By similarity). May play a role as a negative regulator of cell growth. Inhibits cell proliferation. {ECO:0000250|UniProtKB:Q9JLP1, ECO:0000250|UniProtKB:Q9R226, ECO:0000269|PubMed:10564820, ECO:0000269|PubMed:15901763, ECO:0000269|PubMed:19561594, ECO:0000269|PubMed:26758068}. (Microbial infection) Involved in post-transcriptional regulation of HIV-1 gene expression. .