The level of transcription from the promoter of the microcin C51 operon (Pmcc) depends on the growth phase of Escherichia coli cells transcription proceeds with low efficiency at the exponential phase of growth and with higher efficiency when growth of cells is delayed during entry into the stationary phase. The functioning of Pmcc was studied in cells giown in different media by a single-copy construct, which contained the cloned promoter region of the microcin C51 operon and the promoterless lac operon. A decrease in the rate of cell growth caused by changes in the sole carbon source in minimal medium correlated with an increase in the level of transcription fiom the Pmcc promoter at the exponential phase of growth, the expression of Pmcc-lac during cell entry into the stationary phase was higher under less favorable medium conditions. The use of composite rich media impaired this feature. The addition of 1-leucine (100 μg/ml) to the medium decreased the expression of Pmcc-lac in wild-type cells and those carrying the Δlip mutation. A further increase in leucine concentration and the presence of other amino acids in the medium enhanced transcription that started from Pmcc during cell entry into the stationary growth phase. The capacity of the Pmcc promoter and of the wild-type lacZgene promoter upon IPTG induction was virtually the same. A mutation in the ompR gene did not markedly influence transcription started from Pmcc.
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