Yolk polypeptide processing in the fat body ofSarcophaga bullata

In Sarcophaga bullata there are at least three genes coding for the major yolk polypeptides. By means of the reticulocyte cell-free translation system in combination with dog pancreatic microsomal membranes, it was demonstrated that minor processing of the peptides occurs in Sarcophaga. Prior to secretion, only the cleavage of the signal peptide is observed. In vitro translation experiments also revealed that Sarcophaga males require only 20-hydroxyecdysone and not juvenile hormone for the induction of the yolk polypeptide transcription. Following a single injection of 20-hydroxyecdysone in males, in vivo pulse labeling experiments showed that translation of the yolk polypeptides continues for no longer than 24–36 h; only a continuous stimulation by 20-hydroxyecdysone results in prolonged synthesis of the yolk polypeptides.