RESUMO
Transfer RNA modification improves the rate of aa-tRNA selection at the A-site and the fitness in the P-site and thereby prevents frameshifting according to a new model how frameshifting occurs [Qian et al. (1998) Mol. Cell 1, 471-482]. Evidence that the presence of various modified nucleosides in tRNA also influences central metabolism, thiamine metabolism, and bacterial virulence is reviewed.
Assuntos
Mudança da Fase de Leitura do Gene Ribossômico/fisiologia , RNA de Transferência/metabolismo , Mudança da Fase de Leitura do Gene Ribossômico/genética , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , RNA de Transferência/genéticaRESUMO
The modified nucleoside 2-methylthio-N-6-isopentenyl adenosine (ms2i6A) 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 (ms2io6A; also referred to as 2-methylthio cis-ribozeatin) is found in tRNA, most likely in the species that have ms2i6A in E. coli. Mutants (miaE) of S. typhimurium in which ms2i6A 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 ms2io6A37 and is not due to a second cellular function of tRNA (ms2io6A37)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.
Assuntos
Ciclo do Ácido Cítrico , Isopenteniladenosina/análogos & derivados , RNA de Transferência/química , RNA de Transferência/genética , Salmonella typhimurium/genética , Salmonella typhimurium/metabolismo , Mapeamento Cromossômico , Fumaratos/metabolismo , Genes Bacterianos , Teste de Complementação Genética , Isopenteniladenosina/química , Malatos/metabolismo , Mutação , Fenótipo , RNA de Transferência/metabolismo , Salmonella typhimurium/crescimento & desenvolvimento , Ácido Succínico/metabolismoRESUMO
Lysine-agarose provides a simple means of separating RNA species of different moleecular weight. When RNA from Escherichia coli is added to a small column of lysine-agarose and elution is carried out at neutral pH with a shallow linear gradient of NaCl the RNA species are eluted according to size; 4S and 5S RNA species are completely separated and after a delay the 16S and 23S species are eluted as separate peaks. The process is very reproducible and the different species are eluted at a fixed salt concentration even when changes are made in the gradient, provided other conditions, under which the column is run remain constant.
