THE RELATED ADHESION FOCAL TYROSINE KINASE FORMS A COMPLEX WITH PAXILLIN IN HEMATOPOIETIC-CELLS

Related adhesion focal tyrosine kinase (RAFTK), also known as proline- rich tyrosine kinase 2 and cellular adhesion kinase beta, has been rec ently cloned and characterized as a member of the focal adhesion kinas e (FAR) subfamily. RAFTK has an overall 48% amino acid homology to p12 5(FAK) and contains a kinase domain but lacks a transmembrane region, myristylation sites, and Src homology region 2 and 3 domains. By North ern blot analysis, RAFTK is expressed in myeloid, lymphoid, and megaka ryocytic hematopoietic cells. Like p125(FAK), we found that RAFTK inte racts with the focal adhesion protein paxillin. In the lymphoid cell l ine BaF3 and the myeloid cell Line 32Dc13, RAFTK coprecipitates with p axillin. Using in vitro binding assays, RAFTK and paxillin were shown to bind directly, through a segment of paxillin that required amino ac ids 100-227 and a domain in the C terminus of RAFTK. In vitro, RAFTK c ould phosphorylate paxillin on tyrosine residues, These results sugges t that RAFTK, as well as p125(FAK), may be important in phosphotyrosin e-signaling events within the focal adhesion.