IDENTIFICATION OF AN ABL-RELATED PROTEIN-TYROSINE KINASE IN THE CORTEX OF THE SEA-URCHIN EGG - POSSIBLE ROLE AT FERTILIZATION

Fertilization results in the tyrosine phosphorylation of several egg p roteins within minutes of sperm-egg binding, although the identity of the kinase(s) involved and the mechanism of regulation is not known. I n the present study, we have used site-directed antibodies based on th e predicted amino acid sequence of a sea urchin egg transcript that sh ares significant homology with members of the ABL family of protein ty rosine kinases. These antibodies identified a 220-kDa protein kinase, highly enriched in the egg cortex, where it is tightly associated with detergent-insoluble cytoskeletal elements. The enzyme is capable of p hosphorylating synthetic peptide substrates which were used to charact erize the kinase activity in an immune-complex assay. Measurement of t he protein tyrosine kinase activity immunoprecipitated at different ti mes after fertilization revealed that the level of kinase activity is transiently elevated during the first few minutes postinsemination. We stern blot analysis indicated that the amount of the 220-kDa protein d id not increase significantly during this period, so the increased kin ase activity probably results from activation of the enzyme. These in vitro studies indicate that the 220-kDa abl-related kinase is one of t he protein kinases activated during fertilization and suggest that it may play a role in the egg activation process. (C) 1994 Academic Press , Inc.