This is the RNA recognition motif 1 (RRM1) in serine/arginine (SR) proteins serine/arginine-rich splicing factor 4 (SRSF4 or SRp75 or SFRS4) and serine/arginine-rich splicing factor 5 (SRSF5 or SRp40 or SFRS5 or HRS), and related proteins. SRSF4 plays an important role in both constitutive and alternative, splicing of many pre-mRNAs [, ]. It can shuttle between the nucleus and cytoplasm. SRSF5 regulates both alternative splicing and basal splicing []. It is the only SR protein efficiently selected from nuclear extracts (NE) by the splicing enhancer (ESE) and essential for enhancer activation. Members in this family contain two N-terminal RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), followed by a C-terminal RS domains rich in serine-arginine dipeptides [].
