MUTATIONAL ANALYSIS OF THE DROSOPHILA SNAKE PROTEASE - AN ESSENTIAL ROLE FOR DOMAINS WITHIN THE PROENZYME POLYPEPTIDE-CHAIN

Two genes involved in the generation of dorsoventral asymmetry in the developing Drosophila melanogaster embryo, snake and easter, encode th e zymogen form of serine proteases. Mutant alleles of snake were clone d and sequenced revealing mio types of lesions: point mutations which alter the amino acid sequence (snk(073) and snk(rm4)) and point mutati ons which alter the splicing (snk(229) or snk(233)) of intron 1 of the mRNA from the normal 3' end of the intron to a cryptic site. snake mu tant embryos derived from homozygous mothers can be fully rescued by i njection of RNA transcripts of the wild-type snake cDNA. RNA phenotypi c rescue and site-directed mutagenesis experiments indicate that snake requires the serine, histidine and aspartic acid of the catalytic tri ad for normal activity. Deletion experiments show that an acidic proen zyme domain is required for snake rescue activity to be uniformly dist ributed throughout the embryo. A second proenzyme domain, called the d isulfide knot, appears to be essential for normal regulation of activi ty of the snake catalytic chain. Transcripts encoding only the proenzy me polypeptides of either snake or easter can dorsalize wild type embr yos. We propose a model in which the proenzyme determinants of both th e snake and easter enzymes mediate interaction between the serine prot eases and other components of the dorsal-ventral patterning system.