MUTATIONAL ANALYSIS OF THE SRC HOMOLOGY-2 DOMAIN PROTEIN-TYROSINE-PHOSPHATASE CORKSCREW

The SRC homology 2 (SH2) domain protein-tyrosine phosphatase, Corkscre w (CSW) is required for signaling by receptor tyrosine kinases, includ ing the Sevenless receptor tyrosine kinase (SEV), which directs Drosop hila R7 photoreceptor cell development, To investigate the role of the different domains of CSW, we constructed domain-specific csw mutation s and assayed their effects on CSW function. Our results indicate that CSW SH2 domain function is essential, but either CSW SH2 domain can f ulfill this requirement. We also found that CSW and activated SEV are associated in vivo in a manner that does not require either CSW SH2 do main function or tyrosine phosphorylation of SEV, In contrast, the int eraction between CSW and Daughter of Sevenless, a CSW substrate, is de pendent on SH2 domain function, These results suggest that the role of the CSW SH2 domains during SEV signaling is to bind Daughter of Seven less rather than activated SEV, We also found that although CSW protei n-tyrosine phosphatase activity is required for full CSW function, a c atalytically inactive CSW is capable of providing partial function, In addition, we found that deletion of either the CSW protein-tyrosine p hosphatase insert or the entire CSW carboxyl terminus, which includes a conserved DRK/GRB2 SH2 domain binding sequence, does not abolish CSW function.