Title: Metabolic regulation of the tryptophan operon of Escherichia coli: Repressor-independent regulation of transcription initiation frequency
Abstract: Examination of the transcriptional and translational yields from the tryptophan operon of Escherichia coli in trpR− (repressor-negative) cultures growing in various media has revealed that expression of the operon is modulated despite the absence of the operon-specific repression system. When trpR− cultures are grown in minimal medium supplemented with various single carbon-energy sources, the rate of synthesis of trp operon mRNA and enzymes varies directly with the cell growth rate. This direct proportionality between cell growth rate and the rate of expression of the operon is not observed when trpR− cultures are grown in glucose minimal medium supplemented with amino acids, or in L-broth. In these “rich” media the rate of synthesis of trp mRNA and trp enzymes is reduced approximately twofold relative to the rate observed in glucose/minimal medium. The depression of the rate of constitutive trp operon expression in both poor and rich media apparently results from some general control(s) which modulate gene expression when cells are in different metabolic states. Experiments are presented which show that this metabolic regulation modulates operon expression by changing the frequency of transcription initiations on the operon. These experiments also show that the average number of ribosomes which translate each trp mRNA molecule is nearly constant over a fourteenfold range of cell growth rates. Findings are presented which suggest that the rate of transcription initiations on the constitutive trp operon may under some circumstances be affected by the availability of RNA polymerase molecules, although other control mechanisms have not been ruled out.
Publication Year: 1972
Publication Date: 1972-08-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 52
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