Alternative route for biosynthesis of amino sugars in Escherichia coli K-12 mutants by means of a catabolic isomerase.
By inserting a lambda placMu bacteriophage into gene glmS encoding glucosamine 6-phosphate synthetase (GlmS), the key enzyme of amino sugar biosynthesis, a nonreverting mutant of Escherichia coli K-12 that was strictly dependent on exogenous N-acetyl-D-glucosamine or D-glucosamine was generated. Analysis of suppressor mutations rendering the mutant independent of amino sugar supply revealed that the catabolic enzyme D-glucosamine-6-phosphate isomerase (deaminase), encoded by gene nagB of the nag operon, was able to fulfill anabolic functions in amino sugar biosynthesis. The suppressor mutants invariably expressed the isomerase constitutively as a result of mutations in nagR, the locus for the repressor of the nag regulon. Suppression was also possible by transformation of glmS mutants with high-copy-number plasmids expressing the gene nagB. Efficient suppression of the glmS lesion, however, required mutations in a second locus, termed glmX, which has been localized to 26.8 min on the standard E. coli K-12 map. Its possible function in nitrogen or cell wall metabolism is discussed.
Vogler
A P
AP
Fachbereich Biologie/Chemie, Universität Osnabrück, Federal Republic of Germany.
Trentmann
S
S
Lengeler
J W
JW
D019747:Aldose-Ketose Isomerases; D002238:Carbohydrate Epimerases / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005798:Genes, Bacterial; D005819:Genetic Markers / Q000032:analysis; D005838:Genotype; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000235:genetics; D006595:Hexosamines / Q000096:biosynthesis*; D009154:Mutation; D009876:Operon; D010641:Phenotype; D010957:Plasmids; D015183:Restriction Mapping; D013489:Suppression, Genetic; D014161:Transduction, Genetic
D005819:Genetic Markers; D006595:Hexosamines; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); C020582:glucosamine-6-phosphate isomerase; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases