INCREASED UNSATURATED FATTY-ACID PRODUCTION ASSOCIATED WITH A SUPPRESSOR OF THE FABA6(TS) MUTATION IN ESCHERICHIA-COLI

Plasmids that corrected the temperature-sensitive unsaturated fatty ac id auxotrophy of strain M6 [fabA6 (Ts)] were isolated from an Escheric hia coli genomic library, Subcloning and physical mapping localized th e new gene (called sfa for suppressor of fabA) at 1,070 kb on the E. c oli chromosome. DNA sequencing revealed the presence of a 227-bp open reading frame which directed the synthesis of a peptide of approximate ly 8 kDa, which correlated with the correction of the fabA6(Ts) phenot ype. However, the sfa gene was an allele-specific suppressor since pla smids harboring the sfa gene corrected the growth phenotype of fabA6(T s) mutants but did not correct the growth of fabA2(Ts) or fabB15(Ts) u nsaturated fatty acid auxotrophs. Overexpression of the sfa gene in fa bA6(Ts) mutants restored unsaturated fatty acid content at 42 degrees C, and overexpression in wild-type cells resulted in a substantial inc rease in the unsaturated fatty acid content of the membrane, Thus, the suppression of the fabA6(Ts) mutation by sfa was attributed to its ab ility to increase the biosynthesis of unsaturated fatty acids.