The effect of antibiotics on the in vivo synthesis of messenger ribonucleic acid from the lactose operon of Escherichia coli.

Abstract

Lac transcription is rapidly reduced to 3–5% of the original value in E. coli cells treated with antibiotics which block protein synthesis in general. Chloramphenicol (CM) exerts the most rapid, streptomycin (Sm) an intermediate, puromycin a slower effect. Cyclic AMP relieves about 15% of the CM-, 20% of the Sm-, and 40–60% of the puromycin effect indicating an increasing role of catabolite repression in the reduction of lac transcription. The remaining effects are due to the arrest of ribosomes on the nascent newly synthesized mRNA (CM and Sm) and probably the release of ribosomes from the RNA after termination of peptide synthesis (puromycin). In both cases mRNA unprotected by ribosomes is synthesized which either becomes rapidly degraded or hinders the further progression of RNA polymerase. Experiments with the polarity suppressor suA+ argue for the rapid degradation. Both, CM and Sm, reduce the total mRNA synthesis of E. coli to only 70%, while lac transcription is reduced to 15–20% (in the absence of catabolite repression). A possible reason for this difference is discussed.