The interaction and colocalization of Sam68 with the splicing-associated factor YT521-B in nuclear dots is regulated by the Src family kinase p59(fyn)

Alternative pre-mRNA splicing patterns can change an extracellular stimulus , but the signaling pathways leading to these changes are still poorly char acterized. Here, we describe a tyrosine-phosphorylated nuclear protein, YT5 21-B, and show that it interacts with the nuclear transcriptosomal componen t scaffold attachment factor B, and the 68-kDa Src substrate associated dur ing mitosis, Sam68. Northern blot analysis demonstrated ubiquitous expressi on, but detailed RNA in situ analysis revealed cell type specificity in the brain. YT521-B protein is localized in the nucleoplasm and concentrated in 5-20 large nuclear dots. Deletion analysis demonstrated that the formation of these dots depends on the presence of the amino-terminal glutamic acid- rich domain and the carboxyl-terminal glutamic acid/arginine-rich region. W e show that the latter comprises an important protein-protein interaction d omain. The Src family kinase p59(fyn)-mediated tyrosine phosphorylation of Sam68 negatively regulates its association with YT521-B, and overexpression of p59(fyn) dissolves nuclear dots containing YT521-B. In vivo splicing as says demonstrated that YT521-B modulates alternative splice site selection in a concentration-dependent manner. Together, our data indicate that YT521 -B and Sam68 may be part of a signal transduction pathway that influences s plice site selection.