Serine/arginine-rich protein 75 (SRp75) is encoded by the SRSF4 gene. SRp75 belongs to the arginine/serine-rich factor family and likely plays a role in alternative mRNA splicing.The family of SR factors all contain one or more RNA recognition motifs (RRM) and an arginine/ serine (RS)-rich domain. They are not only essential for constitutive splicing but also regulate splicing in a concentration-dependent manner by influencing the selection of alternative splice sites. The majority of SR proteins, including SC35 and SRp40, are confined to the nucleus, while SF2/ASF, SRp20, and 9G8 are continuously shuttled between the nucleus and the cytoplasm and contribute to mRNA transport. The activity of SR proteins in regulated splicing is antagonized by members of the hnRNP A/B family of proteins, which induce drastic shifts in the selection of splicing sites.