STAP-2 is a protein that contains a pleckstrin homology (PH) domain and an SH2 domain, and associates with BRK. BRK (breast tumor kinase, Sik) is a 451 amino acid, nonreceptor protein-tyrosine kinase that is overexpressed in breast tumors and metastatic melanoma cell lines. Similar to the Src family of intracellular kinses, BRK is comprised of an SH3 domain, an SH2 domain, and a catalytic domain. STAP-2 is susceptiple to tyrosine phosphorylation and may be invovled in tyrosine kinase-mediated signaling cascades, whose aberrant function may lead to metastis.