PNN Interacting Serine/Arginine Rich Protein (PNISR)

Pnn colocalized and copurified with serine-arginine (SR) proteins. Three SR-rich proteins were identified that interact with the C-terminus of Pnn: SRp75 and SRm300, known components of spliceosome machinery, and a novel 130-kDa nuclear protein, SRrp130. All of these proteins colocalized and coimmunoprecipitated with one another and exhibited speckled nuclear distribution that aligned with components of the pre-mRNA splicing machinery. The cDNA for SRrp130 encoded a protein of 805 amino acid residues and contained multiple arginine-serine (RS) repeats but had no RNA recognition motif. Analysis of the Pnn motifs using two-hybrid system assays demonstrated that the polyserine/RS motif within Pnn plays a central but not exclusive role in mediating molecular interactions with identified SR-rich proteins.