Overexpression of yccL (gnsA) andydfY (gnsB) Increases Levels of Unsaturated Fatty Acids and Suppresses both the Temperature-SensitivefabA6 Mutation and Cold-SensitivesecG Null Mutation of Escherichia coli

ABSTRACT A multicopy suppressor of the cold-sensitive secGnull mutation was isolated. The suppressor containedsfa and yccL, the former of which has been reported to be a multicopy suppressor of the fabA6mutation carried by a temperature-sensitive unsaturated fatty acid auxotroph. Subcloning of the suppressor gene revealed thatyccL, renamed gnsA (secGnull mutant suppressor), was responsible for the suppression of both the secG null mutation and the fabA6mutation. In contrast, the sfa gene did not suppress thefabA6 mutation. The ydfY(gnsB) gene, encoding a protein which is highly similar to GnsA, also suppressed both the secG null mutation and the fabA6 mutation. Although both gnsAand gnsB are linked to cold shock genes, the levels of GnsA and GnsB did not exhibit a cold shock response. AgnsA-gnsB double null mutant grew normally under all conditions examined; thus, the in vivo functions of gnsAand gnsB remain unresolved. However, overexpression of gnsA and gnsBstimulated proOmpA translocation of the secG null mutant at low temperature and caused a significant increase in the unsaturated fatty acid content of phospholipids. Taken together, these results suggest that an increase in membrane fluidity due to the increase in unsaturated fatty acids compensates for the absence of the SecG function, especially at low temperature.

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