Relationship between protein synthesis and concentrations of charged and uncharged tRNATrp in Escherichia coli.
We have continuously monitored Trp-tRNA(Trp) concentrations in vivo and, in the same cultures, measured rates of protein synthesis in isogenic stringent and relaxed strains. We have also manipulated cellular charged and uncharged [tRNA(Trp)] by two means: (i) the strain used contains a Trp-tRNA synthetase mutation that increases the Km for Trp; thus, varying exogenous Trp varies cellular Trp-tRNA(Trp); and (ii) we have introduced into the mutant strain a plasmid containing the tRNA(Trp) gene behind an inducible promoter; thus, total [tRNA(Trp)] also can be varied depending on length of induction. The use of these conditions, combined with a previously characterized assay system, has allowed us to demonstrate that (i) the rate of incorporation of Trp into protein is proportional to the fraction of tRNA(Trp) that is charged; for any given total [tRNA(Trp)], this rate is also proportional to the [Trp-tRNA(Trp)]; (ii) uncharged tRNA(Trp) inhibits incorporation of Trp into protein; and (iii) rates of incorporation into protein of at least two other amino acids, Lys and Cys, are also sensitive to [Trp-tRNA(Trp)] and are inhibited by uncharged tRNA(Trp). Our results are consistent with models of translational control that postulate modulating polypeptide chain elongation efficiency by varying concentrations of specific tRNAs.
Rojiani
M V
MV
Department of Microbiology and Molecular Genetics, New Jersey Medical School, Newark 07103.
Jakubowski
H
H
Goldman
E
E
D000604:Amino Acyl-tRNA Synthetases / Q000235:genetics*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D003545:Cysteine / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D009154:Mutation; D010957:Plasmids; D012345:RNA, Transfer, Amino Acid-Specific / Q000378:metabolism*; D012364:RNA, Transfer, Trp / Q000235:genetics / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism; D014369:Tryptophan-tRNA Ligase / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D012345:RNA, Transfer, Amino Acid-Specific; D012364:RNA, Transfer, Trp; D014364:Tryptophan; D000604:Amino Acyl-tRNA Synthetases; D014369:Tryptophan-tRNA Ligase; D008239:Lysine; D003545:Cysteine