THE DROSOPHILA-MELANOGASTER SEX-PEPTIDE - A MOLECULAR ANALYSIS OF STRUCTURE-FUNCTION-RELATIONSHIPS

In Drosophila melanogaster a 36 amino acid sex-peptide elicits the cha racteristic postmating behavior of females: rejection of males and ind uction of ovulation/oviposition. Here we report additional evidence by chemical peptide synthesis. To correlate peptide structure and functi on, a full length peptide and fragments thereof were synthesized, and chemically and enzymatically modified. A Staphylococcus aureus protein A-sex-peptide fusion protein was synthesized in E. coli. Based on our results obtained from bioassays we conclude: (1) The N-terminal 7 ami no acids are not needed for sex-peptide function, whereas the disulfid e bridge appears essential. (2) The C-terminal region (encoded by the second exon) is not sufficient. (3) No amino acid modifications are ne eded for sex-peptide action. (4) The potential trypsin cleavage site i s not essential. (5) Synthetic fragments elicit either both or neither of the reactions, i.e. the two functions are not separable. (6) The s ame critical concentration of 0.6 pmol sex-peptide/female is needed to elicit rejection and ovulation. (7) All results are consistent with t he assumption of only one target molecule for both reactions which is accessible via hemolymph.