Mutants of Escherichia coli defective in membrane phospholipid synthesis. Phenotypic suppression of sn-glycerol-3-phosphate acyltransferase Km mutants by loss of feedback inhibition of the biosynthetic sn-glycerol-3-phosphate dehydrogenase.
Revertants of Escherichia coli mutants defective in the first enzyme of membrane phospholipid synthesis, sn-glycerol-3-phosphate (glycerol-P) acyltransferase, were investigated. These glycerol-P acyltransferase mutants, selected as glycerol-P auxotrophs, contained membranous glycerol-P acyltransferase activity with an apparent Km for glycerol-P 10 times higher than the parental activity. The glycerol-P acyltransferase activity was also more thermolabile in vitro than the parental activity. Most revertants no longer requiring glycerol-P for growth regained glycerol-P acyltransferase activity of normal thermolability and apparent Km for glycerol-P. However, two novel revertants were isolated which retained an abnormal glycerol-P acyltransferase activity. The glycerol-P dehydrogenase activities of these novel revertants were about 20-fold less sensitive to feedback inhibition by glycerol-P. The feedback-resistant glycerol-P dehydrogenase co-transduced with gpsA, the structural gene for the glycerol-P dehydrogenase. Further transduction experiments demonstrated that the feedback resistant glycerol-P dehydrogenase phenotypically suppressed the glycerol-P acyltransferase Km lesion. The existence of the class of glycerol-P auxotrophs which owe their phenotype to the glycerol-P acyltransferase Km lesion therefore depends on the feedback regulation of glycerol-P synthesis in E. coli.
D000217:Acyltransferases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000378:metabolism*; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D010641:Phenotype; D013045:Species Specificity; D014161:Transduction, Genetic
D005993:Glycerolphosphate Dehydrogenase; D000217:Acyltransferases; D005992:Glycerol-3-Phosphate O-Acyltransferase