Gene regulation by H-NS as a function of growth conditions depends on chromosomal position in Escherichia coli.
Bottom Line: Our results show that the activity of the Phns promoter depends on whether it is placed within the AT-rich regions of the genome that are known to be bound preferentially by H-NS.This modulation of gene expression moreover depends on the growth phase and the growth rate of the cells, reflecting the changes taking place in the relative abundance of different nucleoid proteins and the inherent heterogeneous organization of the nucleoid.Genomic position can thus play a significant role in the adaptation of the cells to environmental changes, providing a fitness advantage that can explain the selection of a gene's position during evolution.
Affiliation: LBPA, UMR 8113 du CNRS, Ecole Normale Supérieure de Cachan, Cachan, France School of Engineering and Science, Jacobs University Bremen, Bremen, Germany.Show MeSH
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Mentions: The reporter construction, comprising the Phns promoter upstream of the YFP gene next to an antibiotic resistance cassette, was inserted at six sites along the genome in three sets of mirror sites on each side of the origin of replication (Figure 1 and Table 1). Gene expression from the hns promoter is mainly regulated by FIS and the H-NS protein itself (Ueguchi et al. 1993; Falconi et al. 1993, 1996); therefore, these reporter strains can be used to measure the relative changes in activity of these two nucleoid proteins along the chromosome as a function of growth phase and growth rate. The strains containing the reporter construct in different positions were grown in a 96-well plate overnight to monitor the changes in OD and fluorescence as a function of time in growth media of different composition resulting in different growth rates. To control for the emergence of heterogeneity in the bacterial population, possibly leading to a decreased average amount of measured fluorescence from YFP, the amount of fluorescence per cell was also measured in parallel experiments by flow cytometry, for cells growing in exponential phase, in a flask, in a shaking incubator, confirming the results obtained in the plate reader (Supporting Information, Figure S1).
Affiliation: LBPA, UMR 8113 du CNRS, Ecole Normale Supérieure de Cachan, Cachan, France School of Engineering and Science, Jacobs University Bremen, Bremen, Germany.