FIG 5.

Summary. Orange arrows show translation effects, and blue arrows show transcription effects. (A) In the absence of translation limitation, the amount of RNAP available is regulated in part by its partition between ribosomal and nonribosomal promoters by the changes in ppGpp and the ensuing transcription rate of ribosomal promoters. (B) The decrease in ribosome processivity by inhibitors such as chloramphenicol (Cm) increases the probability of mRNA degradation, thus penalizing the expression of longer genes and of genes at the end of operons. RNAP subunits β and β' are among the longest genes in E. coli and are found one after the other within the same operon, while ribosomal proteins are among the shortest genes. The decrease in free RNAP can be measured by a decreasing ratio of high-affinity to low-affinity promoter gene expression rate. In nutrient-poor media, inhibition of ribosome activity by chloramphenicol increases the pool of amino acids and decreases the levels of ppGpp, increasing both ribosome production and ribosome activity. Ab, antibiotic.