SR-25, otherwise known as ADP-ribosylation factor-like factor 6-interacting protein 4, is expressed in virtually all tissues. At the N-terminus there is a repeat of serine-arginine (SR repeat), and towards the middle of the protein there are clusters of both serines and of basic amino acids. The presence of many nuclear localisation signals strongly implies that this is a nuclear protein that may contribute to RNA splicing [1]. SR-25 is also implicated, along with heat-shock-protein-27, as a mediator in the Rac1 (GTPase ras-related C3 botulinum toxin substrate 1) signalling pathway [2].

1: Molecular cloning and expression analysis of a putative nuclear protein, SR-25. Sasahara K, Yamaoka T, Moritani M, Tanaka M, Iwahana H, Yoshimoto K, Miyagawa J, Kuroda Y, Itakura M; Biochem Biophys Res Commun. 2000;269:444-450. PMID:10708573

2: Dominant negative Rac1 attenuates paclitaxel-induced apoptosis in human melanoma cells through upregulation of heat shock protein 27: a functional proteomic analysis. Lee SC, Sim N, Clement MV, Yadav SK, Pervaiz S; Proteomics. 2007;7:4112-4122. PMID:17952876