| The interaction and colocalization of Sam 68 with the splicing associated factor YT 521 B in nuclear dots is regulated by the Src family kinase p 59 ( fyn ) . ^^^ Here , we describe a tyrosine phosphorylated nuclear protein , YT 521 B , and show that it interacts with the nuclear transcriptosomal component scaffold attachment factor B , and the 68 kDa Src substrate associated during mitosis , Sam 68 . ^^^ The Src family kinase p 59 ( fyn ) mediated tyrosine phosphorylation of Sam 68 negatively regulates its association with YT 521 B , and overexpression of p 59 ( fyn ) dissolves nuclear dots containing YT 521 B . ^^^ |