Project Summary/Abstract: The splicing of mRNA is a complex biological process that enormously enhances the diversity of proteins within a limited set of protein-coding genes in the cell. While integral for normal function, errors in splicing can occur and lead to various diseases including muscular dystrophy, Alzheimer's disease, parkinsonism, cardiovascular disease, ataxias and cancers. Splicing relies on essential factors known as SR proteins that bind precursor mRNA and then selectively incorporate other protein/RNA elements ultimately leading to a macromolecular machine known as the spliceosome that performs the necessary excision of certain non-coding elements. The SRPKs are a family of protein kinases that phosphorylate and direct SR proteins to the nucleus where they participate in these essential splicing functions. Although much is known about SRPK function in the cytoplasm, less is known about their role in the nucleus. Furthermore, although SRPKs are best known for their role in splicing, we showed recently that SRPK1 phosphorylates protamines, thereby regulating protamine-to-histone exchange on the paternal genome upon fertilization. We will investigate how SRPK1 forms a complex with a second protein kinase in the nucleus to activate the phosphorylation and release of SR proteins and the U1 snRNP component U1-70K for splicing function. We will also explore how SRPK1 uses a novel recognition mechanism compared to SR proteins to phosphorylate protamines and induce DNA phase transitions and genomic decondensation necessary for oocyte development. These studies will involve a broad range of biophysical and biological techniques including mass spectrometry, molecular and cell biology, enzyme kinetics, and confocal microscopy. Overall, the experiments outlined in this proposal will address the key functions of the protein kinase SRPK1 in controlling protein diversity as well as at the earliest stages of life.