SsrA-mediated protein tagging in the presence of miscoding drugs and its physiological role in Escherichia coli.
BACKGROUND
We have shown recently that read-through of a normal stop codon by a suppressor tRNA in specific genes possessing a Rho-independent terminator leads to SsrA-mediated tagging of extended proteins in Escherichia coli cells. Miscoding antibiotics such as kanamycin and streptomycin reduce translational fidelity by binding to the 30S ribosomal subunit. The aim of the present study was to address how miscoding antibiotics affect the read-through of stop codons and SsrA-mediated protein tagging.


RESULTS
Miscoding antibiotics caused translational read-through of stop codons when added to the culture medium at sublethal concentrations. Under the same conditions, the drugs enhanced SsrA-mediated tagging of bulk cellular proteins, as observed in cells carrying an ochre suppressor tRNA. Translational read-through products generated from the crp gene in the presence of the antibiotics was efficiently tagged by the SsrA system, presumably because the ribosome reached the 3' end of the mRNA defined by the terminator hairpin. The SsrA-defective cells were more sensitive to the miscoding antibiotics compared to the wild-type cells.


CONCLUSIONS
We conclude that the SsrA system contributes to the survival of cells by dealing with translational errors in the presence of low concentrations of miscoding antibiotics.
Abo
Tatsuhiko
T
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
Ueda
Koji
K
Sunohara
Takafumi
T
Ogawa
Kazuko
K
Aiba
Hiroji
H
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D029968:Escherichia coli Proteins; D016601:RNA-Binding Proteins; C430328:small protein B