Genetic determination of sn-glycerol-3-phosphate dehydrogenase synthesis in Drosophila melanogaster. A cis-acting controlling element.

A variant that uniformly reduces the activity of larval and adult isozymes of sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) throughout development has been isolated and analyzed. This low activity line (BI 114), which bears the fast electrophoretic structural allele, has been analyzed in comparison with two high activity control lines, WGM 74 (fast electrophoretic variant) and RI09 (slow electrophoretic variant). The enzyme has been purified from each line and all three variants have similar kinetic, immunological, and physicochemical parameters, except for pI differences associated with the electrophoretic differences observed. Enzyme-specific cross-reacting material analysis corroborates the activity data indicating differential rates of enzyme accumulation between lines throughout development. Protein turnover studies indicate that the rate of intracellular degradation between lines is the same, and that the activity and enzyme-specific cross-reacting material differences observed are due to differential rates of synthesis of the enzyme. Genetic analysis indicates that the variation in the rate of glycerol phosphate dehydrogenase synthesis segregates as a single gene with additive inheritance and is closely linked to the structural gene. Zymogram analysis of F1 heterozygotes has indicated that the variant acts as a cis-regulator and affects both isozymes equally throughout development. We have therefore designated this variant as a systemic regulator controlling the rate of glycerol phosphate dehydrogenase synthesis.