DROSOPHILA-MELANOGASTER ACETYLCHOLINESTERASE - IDENTIFICATION AND EXPRESSION OF 2 MUTATIONS RESPONSIBLE FOR COLD-SENSITIVE AND HEAT-SENSITIVE PHENOTYPES

Ace(IJ29) and Ace(IJ29) are cold- and heat-sensitive variants of the g ene coding for acetylcholinesterase in Drosophila melanogaster. In the homozygous condition, these mutations are lethal when animals are rai sed at restrictive temperatures, i.e., below 23 degrees C for Ace(IJ29 ) or above 25 degrees C for Ace(IJ40). The coding regions of the gene in these mutants were sequenced and mutations changing Ser(374) to Phe in Ace(IJ29) and pro(75) to Leu in Ace(IJ40) were found. Acetylcholin esterases bearing these mutations were expressed in Xenopus oocytes an d we found that these mutations decrease the secretion rate of the pro tein most probably by affecting its folding. This phenomenon is exacer bated at restrictive temperatures decreasing the amount of secreted ac etylcholinesterase below the lethality threshold. In parallel, the sub stitution of the conserved Asp(248) by an Asn residue completely inhib its the activity of the enzyme and its secretion, preventing the corre ct folding of the protein in a non-conditional manner.