The DeoR-type transcriptional regulator SugR acts as a repressor for genes encoding the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Corynebacterium glutamicum
Background: The major uptake system responsible for the transport of fructose, glucose, and
sucrose in Corynebacterium glutamicum ATCC 13032 is the phosphoenolpyruvate:sugar
phosphotransferase system (PTS). The genes encoding PTS components, namely ptsI, ptsH, and ptsF
belong to the fructose-PTS gene cluster, whereas ptsG and ptsS are located in two separate regions
of the C. glutamicum genome. Due to the localization within and adjacent to the fructose-PTS gene
cluster, two genes coding for DeoR-type transcriptional regulators, cg2118 and sugR, are putative
candidates involved in the transcriptional regulation of the fructose-PTS cluster genes.
Results: Four transcripts of the extended fructose-PTS gene cluster that comprise the genes sugRcg2116,
ptsI, cg2118-fruK-ptsF, and ptsH, respectively, were characterized. In addition, it was shown
that transcription of the fructose-PTS gene cluster is enhanced during growth on glucose or
fructose when compared to acetate. Subsequently, the two genes sugR and cg2118 encoding for
DeoR-type regulators were mutated and PTS gene transcription was found to be strongly enhanced
in the presence of acetate only in the sugR deletion mutant. The SugR regulon was further
characterized by microarray hybridizations using the sugR mutant and its parental strain, revealing
that also the PTS genes ptsG and ptsS belong to this regulon. Binding of purified SugR repressor
protein to a 21 bp sequence identified the SugR binding site as an AC-rich motif. The two
experimentally identified SugR binding sites in the fructose-PTS gene cluster are located within or
downstream of the mapped promoters, typical for transcriptional repressors. Effector studies using
electrophoretic mobility shift assays (EMSA) revealed the fructose PTS-specific metabolite
fructose-1-phosphate (F-1-P) as a highly efficient, negative effector of the SugR repressor, acting in
the micromolar range. Beside F-1-P, other sugar-phosphates like fructose-1,6-bisphosphate (F-1,6-
P) and glucose-6-phosphate (G-6-P) also negatively affect SugR-binding, but in millimolar
concentrations