Protein turnover in adult Drosophila

Abstract

Adult male Drosophila subobscura were pulse-labelled with 3H leucine, and radioactivity incorporated into protein measured for 20 days after the pulse label, by extracting total protein and by autoradiography. The halflife of these proteins which turn over in the adult is approximately 10 days. The rate of synthesis varies greatly between tissues, being greatest in the wall of the mid-gut and almost zero in thoracic flight muscle. Larvae were raised axenically in a medium containing labelled amino acids, and the radioactivity in protein followed for 60 days after emergence by extracting total protein, and for 25 days by autoradiographs. The activity in total protein declined rapidly during the first 4 days after emergence of adults, and then remained constant. Autoradiographs suggest that the initial drop is largely due to the disappearance of the pupal fat body, which contains a large amount of protein at emergence. Ignoring storage protein in the fat body, approximately 20 per cent of the total protein in the adult male turns over, with a half-life of approximately 10 days, and the remaining 80 per cent is not replaced. Among the non-replaced proteins are the structural and mitochondrial proteins of the flight muscles. There is active synthesis of ribosomal proteins.