Open AccessHow to achieve constitutive expression of a gene within an inducible operon: the example of the nagC gene of Escherichia coli
Author(s) -
Jacqueline Plumbridge
Publication year - 1996
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.178.9.2629-2636.1996
Subject(s) - biology , operon , gene , promoter , repressor , transcription (linguistics) , messenger rna , gene expression , microbiology and biotechnology , regulon , regulation of gene expression , escherichia coli , genetics , linguistics , philosophy
The nagC gene, encoding the NagC repressor/activator of the nag regulon, is part of the nagBACD operon. When the promoter-proximal nagB and nagA genes are induced 20- to 40-fold, the nagC gene is induced only two- to threefold. In addition to being transcribed as part of the polycistronic nagBACD mRNA, nagC is also expressed from two promoters located within the upstream nagA gene. These promoters are comparable in strength to the induced nagB promoter, resulting in a high basal level of the nagC mRNA. This means that when the nagBA genes are induced, there is a much smaller effect on the amount of nagC mRNA. The nagC gene is subject to low-level translation so that the amount of NagC protein is kept low despite the relatively high transcription levels.