The EIIGlc protein is involved in glucose-mediated activation of Escherichia coli gapA and gapB-pgk transcription

The Escherichia coli gapB gene codes for a protein that is very similar to bacterial glyceraldehyde-3-phosphate dehydrogenases (GAPDH). In most bacter ia, the gene for GAPDH is located upstream of the pgk gene encoding 3-phosp hoglycerate kinase (PGK). This is the case for gapB, However, this gene is poorly expressed and encodes a protein with an erythrose 4-phosphate dehydr ogenase activity (E4PDH). The active GAPDH is encoded by the gapA gene. Sin ce we found that the nucleotide region upstream of the gapB open reading fr ame is responsible for part of the PGK production, we analyzed gapB promote r activity in vivo by direct measurement of the mRNA levels by reverse tran scription. We showed the presence of a unique transcription promoter, gapB P0, with a cyclic AMP (cAMP) receptor protein (CRP)-cAMP binding site cente red 70.5 bp upstream of the start site. Interestingly, the gapB PO promoter activity was strongly enhanced when glucose was used as the carbon source. In these conditions, deletion of the CRP-cAMP binding site had little effe ct on promoter gapB P0 activity. In contrast, abolition of CRP production o r of cAMP biosynthesis (crp or cya mutant strains) strongly reduced promote r gapB PO activity. This suggests that in the presence of glucose, the CRP- cAMP complex has an indirect effect on promoter gapB PO activity. We also s howed that glucose stimulation of gapB P0 promoter activity depends on the expression of enzyme IIGlc (EIIGlc), encoded by the ptsG gene, and that the gapA P1 promoter is also activated by glucose via the EIIGlc protein. A si milar glucose-mediated activation, dependent on the EIIGlc protein, was des cribed by others for the pfs operon. Altogether, this shows that when gluco se is present in the growth medium expression of the E. coli genes required for its uptake (pts) and its metabolism (gapA and gapB-pgk) are coordinate ly activated by a mechanism dependent upon the EIIGlc protein.