Modulation of gene expression through chromosomal positioning in Escherichia coli

Microbiology (Reading). 1997 Jun;143 ( Pt 6):2071-8. doi: 10.1099/00221287-143-6-2071.


Variations in expression of the nah genes of the NAH7 (naphthalene biodegradation) plasmid of Pseudomonas putida when placed in different chromosomal locations in Escherichia coli have been studied by employing a collection of hybrid mini-T5 transposons bearing lacZ fusions to the Psal promoter, along with the cognate regulatory gene nahR. Insertions of Psal-lacZ reporters in the proximity of the chromosomal origin of replication, oriC, increased accumulation of beta-galactosidase in vivo. Position-dependent changes in expression of the reporter product could not be associated with local variations of the supercoiling in the DNA region, as revealed by probing the chromosome with mobile gyrB-lacZ elements. Such variations in beta-galactosidase activity (and, therefore, the expression of catabolic genes) seemed, instead, to be linked to the increase in gene dosage associated with regions close to oriC, and not to local variations in chromosome structure. The tolerance of strains to the selection markers borne by the transposons also varied in parallel with the changes in LacZ levels. The role of chromosomal positioning as a mechanism for the outcome of adaptation phenotypes is discussed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biodegradation, Environmental
  • Chromosome Mapping
  • Chromosomes / genetics*
  • DNA Probes / genetics
  • DNA Probes / metabolism
  • DNA Transposable Elements / genetics
  • Escherichia coli / genetics*
  • Gene Expression Regulation, Bacterial / physiology*
  • Genetic Variation
  • Lac Operon / genetics
  • Naphthalenes / metabolism
  • Nucleic Acid Conformation
  • Plasmids / genetics
  • Promoter Regions, Genetic
  • Pseudomonas putida / genetics
  • Replication Origin / genetics


  • DNA Probes
  • DNA Transposable Elements
  • Naphthalenes