IDENTIFICATION OF A BRCA1-ASSOCIATED KINASE WITH POTENTIAL BIOLOGICALRELEVANCE

A biochemical approach was used to identify proteins which interact wi th human BRCA1, Through this work, a kinase activity which co-purifies with BRCA1 has been identified, This kinase activity, which phosphory lates BRCA1 in vitro, was originally identified in Sf9 insect cells bu t is also present in cells of human origin including breast and ovaria n carcinoma cell lines, The BRCA1 kinase activity in vitro is associat ed with a fragment of BRCA1 encompassing amino acids 329-435, This pep tide is also phosphorylated in various human cell lines, A computer-as sisted sequence analysis revealed that this peptide was a potential su bstrate for phosphorylation by PKA, PKC, or CKII, However, phosphoryla tion by these kinases could not be demonstrated in vitro indicating th e presence of another kinase activity, Phosphorylation in vitro requir es a minimal domain of BRCA1 encompassing amino acids 379-408, Notably , deletion of this minimal domain abolishes growth suppression by BRCA 1 indicating that this domain, as well as phosphorylation within this domain, may be important for BRCA1 function.