Expression of RNA polymerase and ribosome component genes in Escherichia coli mutants having conditionally defective RNA polymerases.

The expression of the genes coding for the beta and beta' subunits of RNA polymerase, ribosomal RNA, ribosomal proteins, and beta-galactosidase was investigated in strains carrying conditionally lethal mutations affecting either RNA polymerase core assembly or RNA polymerase enzyme activity. The mutant strain XH56 produces a temperature-sensitive beta' subunit and at 42 degrees C is defective in RNA chain initiation; consequently, little or no transcription occurs at the restrictive temperature. A partial restriction, produced by shifting the strain to 39 degrees C, resulted in a rapid fivefold increase in the transcription of the rpoB and C genes and in the synthesis of the beta- and beta'-subunit proteins for which they code. The RNA polymerase assembly-defective strains A2R7 and TS4 exhibited a 1.5- to 2-fold increase in the transcription of the rpoB and C genes and in the synthesis of beta- and beta-subunit proteins after prolonged restriction. These results demonstrate (i) that regulation of the synthesis of the beta- and beta-RNA polymerase subunits is under these conditions primarily transcriptional rather than translational, and (ii) that a stimulation of rpoB and C gene expression results from a restriction on RNA synthesis caused by either RNA polymerase inactivation or inhibition of its assembly. During restriction of the mutant strains, the transcription of the ribosome component genes exhibited patterns which were similar to transcription of the rpoB and C genes, supporting the evidence that genes coding for RNA polymerase are cotranscribed with ribosomal protein genes; transcription of the lacZ gene was observed to decrease concomitant with the stimulation of the rpoB and C genes.