The
nag genes are an operon in Ralstonia sp. strain U2 that is
regulated by NagR, a LysR-type transcriptional regulator.Jones, R.M., Britt-Compton B.
& Williams P.A. J. Bacteriol. (Submitted)
ABSTRACT
In Ralstonia sp. strain U2, the nag catabolic genes which encode
the enzymes for the pathway that catabolize naphthalene via the alternative
ring-cleavage gentisate pathway are transcribed as an operon under the
same promoter. Divergently transcribed to the nag catabolic genes
is nagR, which encodes a LysR-type transcriptional regulator. A
4 bp frameshift deletion in nagR demonstrated that NagR is required
for the expression of the nag operon. The transcriptional start
of the nag operon was mapped, and a putative -10, -35 sigma 70-type promoter
binding site was identified. Further upstream, a site proximal to the promoter
was identified as having bases which have been found to be conserved in
the LysR-type activator-binding motif. Transcriptional fusion studies demonstrated
that NagR regulates the expression of the nag operon positively in the
presence of salicylate, and to a lesser extent in the presence of 2-nitrobenzoate.
Mutation of the LysR-type activator-binding motif in the nag promoter-proximal
region, resulted in loss of inducibility of a LacZ reporter gene
transcriptionally fused the nagAa, the first gene of the operon.
However other mutations within the region produced elevated levels of
nag gene expression even in the presence of the inducer salicylate.