Properties of the Functioning of the Promoter of the Microcin C51 Operon under Different Conditions of Escherichia coli Cell Growth

Abstract

The level of transcription from the promoter of the microcin C51 operon (P mcc ) depends on the growth phase of Escherichia colicells: 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 P mcc was studied in cells grown in different media by a single-copy construct, which contained the cloned promoter region of the microcin C51 operon and the promoterless lacoperon. 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 from the P mcc promoter at the exponential phase of growth; the expression of P mcc –lacduring 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 l-leucine (100 μg/ml) to the medium decreased the expression of P mcc –lacin wild-type cells and those carrying the Δlrpmutation. A further increase in leucine concentration and the presence of other amino acids in the medium enhanced transcription that started from P mcc during cell entry into the stationary growth phase. The capacity of the P mcc promoter and of the wild-type lacZgene promoter upon IPTG induction was virtually the same. A mutation in the ompRgene did not markedly influence transcription started from P mcc .