title: Hyperinducibility as a result of mutation in structural genes and self-catabolite repression in the ara operon.
abstract: Mutations in gene araB producing an l-arabinose-negative phenotype cause either an increase (hyperinducible), decrease (polar), or have no effect at all on the inducible rate of expression of the l-arabinose operon. Fourteen araB gene mutants exhibiting such effects were shown to be the result of: nonsense, frameshift, or missense mutations. All missense mutants were hyperinducible, exhibiting approximately a twofold increase in rate of l-arabinose isomerase production. All frameshift and most nonsense mutants exhibited polar effect. One nonsense mutant was hyperinducible. The cis-dominant polar effect of nonsense and frameshift mutants (as compared to induced wild type) were more pronounced in arabinose-utilizing merodiploids and in araBaraC(c) double mutants where inducible and constitutive enzyme levels are respectively determined. On the other hand, in arabinose-utilizing merodiploids, missense mutations no longer exhibited hyperinducibility but displayed a wild-type level of operon expression. Increases in the wild type-inducible rate of expression of the operon were found when growth rate was dependent on the concentration of l-arabinose. Cyclic 3',5'-adenosine monophosphate also stimulated expression of the operon with the wild type in a mineral l-arabinose medium. These observations are explained on the basis that the steady-state expression of the l-arabinose operon OIBAD is dependent on the concentration of (i) l-arabinose, the effector of this system, which stimulates the expression of the operon, and (ii) catabolite repressors, produced from l-arabinose, which dampen the expression of the operon. We have termed the latter phenomenon "self-catabolite" repression.
mesh_terms: D001089:Arabinose / Q000378:metabolism* / Q000494:pharmacology; D002874:Chromosome Mapping; D003090:Coliphages; D003470:Culture Media; D000242:Cyclic AMP / Q000494:pharmacology; D004790:Enzyme Induction; D004794:Enzyme Repression; D004926:Escherichia coli / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D005796:Genes; D005816:Genetic Complementation Test; D005827:Genetics, Microbial; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007535:Isomerases / Q000096:biosynthesis / Q000378:metabolism*; D008962:Models, Theoretical; D009153:Mutagens; D009154:Mutation; D010770:Phosphotransferases / Q000378:metabolism; D013045:Species Specificity; D013237:Stereoisomerism; D014161:Transduction, Genetic
chemical_list: D003470:Culture Media; D009153:Mutagens; D001089:Arabinose; D000242:Cyclic AMP; D010770:Phosphotransferases; D007535:Isomerases; D005947:Glucose; D005990:Glycerol