The Ms 2 Io 6 A37 Modification of Trna in Salmonella Typhimurium Regulates Growth on Citric Acid Cycle Intermediates

ABSTRACT 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 Escherichia coli . In Salmonella typhimurium , 2-methylthio- N -6-( cis -hydroxy)isopentenyl adenosine (ms 2 io 6 A; also referred to as 2-methylthio cis -ribozeatin) is found in tRNA, most likely in the species that have ms 2 i 6 A in E. coli . Mutants ( miaE ) of S. typhimurium in which ms 2 i 6 A hydroxylation is blocked are unable to grow aerobically on the dicarboxylic acids of the citric acid cycle. Such mutants have normal uptake of dicarboxylic acids and functional enzymes of the citric acid cycle and the aerobic respiratory chain. The ability of S. typhimurium to grow on succinate, fumarate, and malate is dependent on the state 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. typhimurium senses the hydroxylation status of the isopentenyl group of the tRNA and will grow on succinate, fumarate, or malate only if the isopentenyl group is hydroxylated.