title: pH-sensitive CDP-diglyceride synthetase mutants of Escherichia coli: phenotypic suppression by mutations at a second site.
abstract: In Escherichia coli, mutations which lower the level of CDP-diglyceride synthetase are designated cds and map at min 4. The cds-8 mutation resulted in strikingly defective enzyme activity and also rendered cells pH sensitive for growth. Both the inhibition of growth and the massive accumulation of phosphatidic acid which occur in a cds-8 mutant at pH 8 were suppressed by mutations at a second locus, designated cdsS, which mapped between argG and gltB near min 68. The cdsS3 mutation by itself did not affect CDP-diglyceride synthetase activity in wild-type cells, but it caused a twofold stimulation of the residual activity present in strains harboring cds-8. Both the insensitivity to pH and the twofold stimulation of residual activity were lost by introduction of an F' strain carrying cdsS+ into a recA1 cds-8 cdsS3 host. When a culture of a cds-8 cdsS+ strain was shifted to pH 8, the residual specific activity of synthetase dropped by 75% within 100 min. In a cds-8 cdsS3 double mutant under the same conditions, the activity declined appreciably less, about to the level found in the cds-8 cdsS+ strain under permissive conditions (pH 6). Thus, it appears that mutations in the cdsS gene suppress the pH sensitivity of cds mutants by inhibiting the decay of residual CDP-diglyceride synthetase activity at the nonpermissive pH. The cdsS locus appears to be distinct from any known nonsense or missense suppressor.
mesh_terms: D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D003227:Conjugation, Genetic; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial; D005799:Genes, Dominant; D008040:Genetic Linkage; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism; D013489:Suppression, Genetic
chemical_list: D010712:Phosphatidic Acids; D009713:Nucleotidyltransferases; C022348:phosphatidate cytidylyltransferase