SPATIAL REGULATION OF DROSOPHILA SNAKE PROTEASE ACTIVITY IN THE GENERATION OF DORSAL-VENTRAL POLARITY

Positional information along the dorsal-ventral axis of the Drosophila embryo is acquired through a signal transduction pathway which employ s a extracellular protease cascade. The sequential activation of serin e protease zymogens results in the ventrally localized production of a ligand in the perivitelline space of the embryo. Snake is one of seve ral serine proteases which function in generating the ventralizing sig nal. Here,,ve investigate the biochemical properties of Snake in vivo and in vitro using recombinant forms of the protease. Wild-type Snake zymogen completely rescues embryos from snake null females when microi njected into the perivitelline space. Biochemical evidence for a coval ently associated two-chain form of the activated protease is presented . The contribution of the activation peptide region to zymogen activat ion was addressed using site-directed mutagenesis. The phenotypic resc ue properties of an autoactivated form of Snake reveal that the covale ntly associated proenzyme polypeptide chain suppresses a dominant effe ct associated with the activated catalytic chain alone. Recombinant ac tive catalytic chain was produced and found to be short lived as a rec ombinant protein. These results suggest a model in which the proenzyme polypeptide both stabilizes and targets the Snake catalytic chain to a ventrally localized activation complex within the perivitelline spac e.