Decay of ribonucleic acid synthesis in amino acid starved Escherichia coli after rifampin treatment

The concentration of rifampin necessary to affect the initiation of ribonucleic acid (RNA) synthesis quickly in Escherichia coli strains K-12 and 15TAU was about 200 μg/ml, as determined by extrapolation of the effect of the drug on the induction of β galactosidase synthesis. A lag in the action of rifampin of about 10 s was confirmed. Rifampin was then used as a probe to compare RNA synthesis in growing and amino acid starved E. coli. Restoring arginine to arginine starved strain 15TAU immediately after rifampin inhibition did not detectably restore the rate of uracil uptake to that of uninhibited cells. The residual rate of RNA synthesis (corrected for acid soluble triphosphate specific activities) after rifampin treatment of both growing and isoleucine starved (valine inhibited) cultures of strain K-12 showed similar decay kinetics. These findings support the notion that amino acid starvation blocks the initiation of some RNA transcription units, but do not rule out other possibilities.