Background: Bacterial transfer-messenger RNA (tmRNA, 10Sa RNA) is involved
in a trans-translation reaction which contributes to the degradation of inc
ompletely synthesized peptides and to the recycling of stalled ribosomes. H
owever, its physiological role in the cell remains elusive. In this study,
an efficient system for controlling the expression of the gene for tmRNA (s
srA), as well as a tmRNA gene-defective strain (ssrA::cat), were constructe
d in Bacillus subtilis. The effects of tmRNA on the growth of the cells wer
e investigated under various physiological culture conditions using these s
trains.
Results: The cells were viable in the absence of ssrA expression under the
usual culture conditions. However, the growth rate of cells without tmRNA e
xpression, relative to that of the expressed cells, decreased with elevatin
g temperature (> 45 degrees C), and at 52 degrees C, the highest temperatur
e for growth of the wild-type, cells grew depending on the expression level
of tmRNA. Furthermore, the transcription level of the ssrA from the authen
tic promoter at a high temperature (51 degrees C) was about 10-fold higher
than that at a lower temperature (37 degrees C). tmRNA-dependent growth and
an increase in tmRNA amount were also observed in cells under other stress
es, such as high concentrations of ethanol or cadmium chloride. It is also
shown that alanylated tmRNA rather than tmRNA-mediated proteolysis is requi
red for growth at high temperature.
Conclusion: The expression of tmRNA gene (ssrA) is required for the efficie
nt growth of B. subtilis under several strong stresses. The transcription o
f sstA increases under several stressful conditions, suggesting that it is
a stress-response gene. Alanyl-tmRNA, probably via its ability of recycling
stalled ribosomes via trans-translation, is involved in the stress toleran
ce of bacteria.