THE MS(2)IO(6)A37 MODIFICATION OF TRANSFER-RNA IN SALMONELLA-TYPHIMURIUM REGULATES GROWTH ON CITRIC-ACID CYCLE INTERMEDIATES

The modified nucleoside 2-methylthio-N-6-isopentenyl adenosine (ms(2)i (6)A) is present in position 37 (adjacent to and 3' of the anticodon) of tRNAs that read codons beginning with U except tRNA(I,V)(Ser) in Es cherichia coli, In Salmonella typhimurium , 2-methylthio-N-6-(cis-hydr oxy)isopentenyl adenosine (ms(2)io(6)A; also referred to as 2-methylth io cis-ribozeatin) is found in tRNA, most likely in the species that h ave ms(2)i(6)A in E. coli. Mutants (miaE) of S. typhimurium in which m s(2)i(6)A hydroxylation is blocked are unable to grow aerobically on t he dicarboxylic acids of the citric acid cycle. Such mutants have norm al uptake of dicarboxylic acids and functional enzymes of the citric a cid cycle and the aerobic respiratory chain. The ability of S. typhimu rium Bo grow ore succinate, fumarate, and malate is dependent on the s tate of modification in position 37 of those tRNAs normally having ms( 2)io(6)A37 and is not due to a second cellular function of tRNA (ms(2) io(6)A37)hydroxylase, the miaE gene product. We suggest that S. typhim urium senses the hydroxylation status of the isopentenyl group of the tRNA and will grow on succinate, fumarate, or malate only if the isope ntenyl group is hydroxylated.