When exponentially growing cells of
Bacillus subtilis are exposed to sublethal concentration (0.1μg/ml) of rifampicin, they show an immediate decrease in the rate of RNA synthesis
in vivo, followed by a latent period for 60min, and then a rapid recovery to the original level in 150 min. Cell growth and the viable cell count remained stationary for 90min and then began to increase at a much slower rate. RNA polymerase activity, extracted and assayed
in vitro, followed the same pattern as RNA synthesis
in vivo. The rifampicin-resistant fraction of the RNA-synthesizing activity, and the amount of β
γ subunit, a component of RNA polymerase (RPase) L2, increased with time after incubation in the presence of rifampicin. These results suggested that RPase L2, being a minor rifampicin-resistant fraction of RNA polymerases in normal state, increased several times in rifampicin-treated cultures, so as to make the cells phenotypically resistant to rifampicin.
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