The mglB sequence of Salmonella typhimurium LT2; promoter analysis by gene fusions and evidence for a divergently oriented gene coding for the mgl repressor.
The mglB gene of Salmonella typhimurium LT2 coding for the galactose-binding protein (GBP) was sequenced. We compared the deduced amino acid sequence with the GBP sequence of Escherichia coli K 12. The mature proteins differ in only 19 of 309 amino acid residues, corresponding to 94% homology. Analysis of the mglB control region by promoter-probe vectors revealed that two promoters, P1 and P2, constitute the mgl control region (Pmgl). P1 and P2 function in a synergistic way. P1 is the main promoter of the operon; its activity is 20 times the activity of P2. Both promoters are activated by the cyclic adenosine monophosphate catabolite activator protein (cAMP/CAP) complex. While P1 is inactive in the absence of the cAMP/CAP complex, there is residual activity of P2 under these conditions. Studies on the inducibility of the mglBAEC operon using multicopy plasmid promoter-probe vectors were hampered by the titration of the mgl repressor resulting in a partially constitutive expression of the mgl operon. The results indicate that only P1 is responding to induction by D-fucose. A weak promoter, PD, within the P1 region but divergent to it was found. PD is neither stimulated by the cAMP/CAP complex nor by D-fucose. We cloned the gene located downstream to PD and found it to strongly repress the expression of the mgl operon. We termed this gene mglD. The presence of D-fucose abolished the repression caused by the plasmid-encoded mglD gene product.
Benner-Luger
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Department of Biology, University of Konstanz, Federal Republic of Germany.
Boos
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D000595:Amino Acid Sequence; D001483:Base Sequence; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics; D005690:Galactose; D005796:Genes; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D009876:Operon; D033902:Periplasmic Binding Proteins; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics*; D015183:Restriction Mapping; D012486:Salmonella typhimurium / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C023550:galactose-binding protein; D001616:beta-Galactosidase; D005690:Galactose