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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  sugR-cg2116 ,  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.    Conclusion  In  C. glutamicum  ATCC 13032 the DeoR-type regulator SugR acts as a pleiotropic transcriptional repressor of all described PTS genes. Thus, in contrast to most DeoR-type repressors described, SugR is able to act also on the transcription of the distantly located genes  ptsG  and  ptsS  of  C. glutamicum . Transcriptional repression of the fructose-PTS gene cluster is observed during growth on acetate and transcription is derepressed in the presence of the PTS sugars glucose and fructose. This derepression of the fructose-PTS gene cluster is mainly modulated by the negative effector F-1-P, but reduced sensitivity to the other effectors, F-1,6-P or G-6-P might cause differential transcriptional regulation of genes of the general part of the PTS ( ptsI, ptsH ) and associated genes encoding sugar-specific functions ( ptsF, ptsG, ptsS ).

bmc molecular biology

The DeoR-type transcriptional regulator SugR acts as a repressor for genes encoding the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Corynebacterium glutamicum