Rate of ribosomal ribonucleic acid chain elongation in Escherichia coli B/r during chloramphenicol treatment.

In Escherichia coli B/r growing in glucose-amino acids medium, the radioactive labeling of 5S ribosomal ribonucleic acid (rRNA) and transfer RNA (tRNA) was measured after the simultaneous addition to the bacteria of chloramphenicol (CAM) (100 mug/ml), rifampin (200 mug/ml), and radioactive uracil. Accumulation of 5S rRNA ceased 85 s after the addition of rifampin, independent of the presence or absence of CAM; this indicates that CAM did not affect the rRNA chain growth rate. Together with previous measurements of the synthesis of rRNA and messenger RNA under these conditions, the results imply that CAM caused a redistribution of RNA polymerase which greatly favored stable RNA synthesis (77 to 97% of total functioning RNA polymerase engaged in synthesis of rRNA and tRNA). Further, it is inferred that RNA polymerase molecules were activated that were inactive during exponential growth. The labeling of tRNA observed under these conditions suggests the existence of clusters of tRNA genes at the 3' end of long transcripts that resemble the rRNA precursor in length and response to CAM and may be parts of rRNA transcripts.