SRSF4 (serine and arginine rich splicing factor 4) is a nuclear RNA-binding protein that regulates alternative splicing of pre-mRNA transcripts 1. The protein contains RNA recognition motifs and a serine/arginine-rich domain typical of SR proteins, and localizes to the nucleus via multiple nuclear localization sequences in its RS domain 2. SRSF4 functions as both a splicing activator and repressor depending on the target transcript - it promotes inclusion of Fas exon 6 by binding to a novel enhancer sequence 3, activates CLK1 exon 4 inclusion 4, and regulates RPL22L1 isoform switching in glioblastoma 5. The protein requires phosphorylation for optimal function, as demonstrated in enterovirus A71 infection where phosphorylated SRSF4 facilitates IRES-dependent viral translation 6. SRSF4 has significant disease relevance, contributing to temozolomide resistance in glioma through regulation of DNA double-strand break repair 7, and mutations in SRSF4 cause mitochondrial dysfunction leading to bone marrow failure 8. These findings highlight SRSF4's dual role in normal cellular RNA processing and pathological processes, making it a potential therapeutic target in cancer and genetic disorders.