JBC, Vol. 250, Issue 18, 7153-7158, Sep, 1975
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
R. M. Bell and J. E. Cronan Jr
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.