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Ph sensitive cdp di glyceride synthetase mutants of escherichia coli phenotypic suppression by mutations at a 2nd site

Ph sensitive cdp di glyceride synthetase mutants of escherichia coli phenotypic suppression by mutations at a 2nd site

Journal of Bacteriology 153(2): 731-738

In E. 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. 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 2nd 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 2-fold stimulation of the residual activity present in strains harboring cds-8. Both the insensitivity to pH and the 2-fold 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). Mutations in the cdsS gene apparently 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.

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Accession: 006092015

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