The galactose regulon of Escherichia coli
Article first published online: 27 OCT 2006
Volume 10, Issue 2, pages 245–251, October 1993
How to Cite
Weickert, M. J. and Adhya, S. (1993), The galactose regulon of Escherichia coli. Molecular Microbiology, 10: 245–251. doi: 10.1111/j.1365-2958.1993.tb01950.x
- Issue published online: 27 OCT 2006
- Article first published online: 27 OCT 2006
- Received 17 May, 1993; revised and accepted 6 July, 1993.
Galactose transport and metabolism in Escherichia coli involves a multicomponent amphibolic pathway. Galactose transport is accomplished by two different galactose-specific transport systems. At least four of the genes and operons involved in galactose transport and metabolism have promoters containing similar regulatory sequences. These sequences are recognized by at least three regulators, Gal repressor (GalR), Gal isorepressor (GalS) and cAMP receptor protein (CRP), which modulate transcription from these promoters. The negative regulators, GalR and GalS, discriminate between utilization of the high-affinity (regulated by GalS) and low-affinity (regulated by GalR) transport systems, and modulate the expression of genes for galactose metabolism in an overlapping fashion. GalS is itself autogenously regulated and CRP dependent, while the gene for GalR is constitutive. The gal operon encoding the enzymes for galactose metabolism has two promoters regulated by CRP in opposite ways; one (P1) is stimulated and the other (P2) inhibited by CRP. Both promoters are strongly repressed by GalR but weakly by GalS. All but one of the constituent promoters of the gal regulon have two operators. The gal regulon has the potential to coordinate galactose metabolism and transport in a highly efficient manner, under a wide variety of conditions of galactose availability.