Expression of ptsG, the gene for the major glucose PTS transporter in Escherichia coli, is repressed by Mlc and induced by growth on glucose

Abstract

SummaryThe gene for the glucose-specific transporter of the phosphotransferase system, ptsG, is expressed from two promoters separated by 141 bp. The expression of the major, shorter transcript is very strongly dependent upon cAMP/CAP. However, unlike other CAPactivated genes, the expression of ptsG is higher in glucose media than in glycerol, implying that ptsG is controlled by a glucose-inducible regulator. A mutation in the mlc gene greatly enhances ptsG expression in a glycerol-grown culture but has no effect on ptsG expression during growth on glucose. The mlc gene encodes a transcriptional regulator that has been shown to affect the expression of manXYZ and malT. ptsG mRNA levels are lower in the mlc strain grown on glucose than in the same strain grown on glycerol. This is presumably because of the greater catabolite repression in the glucose culture than in glycerol. The final level of expression of ptsG in a mlc þ strain in glucose is a compromise between specific induction by glucose and generalized catabolite repression. The result is that ptsG expression is very similar in glucose-grown cultures of wild-type and mlc strains. The Mlc protein binds to two sites centred at ¹6 and ¹175 upstream of the major ptsG transcript. CAP binds at ¹40.5 compared with this site, typical of class II CAP-regulated promoters, and the binding of CAP and Mlc is co-operative.

Expression of ptsG Encoding the Major Glucose Transporter Is Regulated by ArcA in Escherichia coli

“…The ArcA-Pbinding site I, which centered at ϩ1.5, overlapped the P1 promoter. It has been well known that the cAMP⅐CRP complex binds to the ptsG promoter centered at Ϫ40.5 and Ϫ95, respectively (15). The binding sites II (centered at Ϫ51.5) and III (centered at Ϫ97.5) of ArcA-P overlapped these two CRP-binding sites, respectively (Fig.…”

“…1, we found that ArcA as well as CRP bound to the two promoter regions, but not to the ORF of ptsG, to a significant level, implying specific binding of these two proteins to the promoter regions. Although it is not surprising that CRP shows specific binding to the two promoters, since its binding sites to the promoters are well characterized (15,18), it is intriguing that ArcA binds specifically to the two promoters.…”

“…It was shown that the ptsH P1 promoter is regulated by the repressor of the fructose PTS, FruR (12). Moreover, both the ptsH P0 promoter and the ptsG P1 promoter have been shown to be subject to activation by the cAMP⅐CRP complex and repression by Mlc (13)(14)(15)(16)(17)(18). Subsequently, it was demonstrated that the unphosphorylated form of EIICB Glc can relieve the repression of the Mlc regulon by sequestering Mlc through the direct protein-protein interaction to induce the expression of the Mlc regulon including PTS proteins (19 -21).…”

Analyses of Mlc–IIB Glc interaction and a plausible molecular mechanism of Mlc inactivation by membrane sequestration

“…Glucose, a representative PTS sugar, mediates transcriptional activation of several genes for PTS-related sugar transporters and some enzymes involved in glycolysis (1, 6). Mlc, a tetrameric protein (7), is a signaling mediator for glucose induction of several PTS operons and related genes (8)(9)(10)(11)(12)(13)(14).A unique feature of induction of the Mlc regulon by glucose is that the effector molecule modulating Mlc activity is a membranebound protein, EIICB Glc (7,15,16), in which cytosolic EIIB protein is attached to membrane-embedded EIIC protein through a linker of Ͼ20 aa. In the absence of glucose, EIICB Glc mainly exists in the phosphorylated form (pEIICB Glc ).…”

“…Glucose, a representative PTS sugar, mediates transcriptional activation of several genes for PTS-related sugar transporters and some enzymes involved in glycolysis (1, 6). Mlc, a tetrameric protein (7), is a signaling mediator for glucose induction of several PTS operons and related genes (8)(9)(10)(11)(12)(13)(14).…”