Specific protein modifications are altered in a temperature-sensitive Drosophila developmental mutant.

The temperature-sensitive Drosophila mutation l(3)c21RRW630 disturbs oogenesis and imaginal disc development and has a maternal effect on embryogenesis. Two-dimensional gel electrophoretic analysis of protein synthesis in mutant tissue at a restrictive temperature shows that the synthesis of three proteins is elevated and the synthesis of three other proteins is reduced, when compared to wild type. Each protein with increased synthesis is similar to a protein whose synthesis is reduced, as judged by comparison of partial proteolytic digests of these proteins. To explain these findings, we propose that the wild-type c21R gene codes for a protein-modifying enzyme. This enzyme catalyzes the acidic modification of three abundant proteins. The correct modification of these proteins is required for cell division, cell motility, and the formation of adult hairs and bristles. In the mutant at restrictive temperature, the enzyme does not function properly and so the unmodified substrate proteins accumulate. This study correlates the morphological defects in a Drosophila developmental mutant with an altered molecular process.