ABSTRACT
Using a multicopy plasmid in which the tac promoter has been placed in front of the dam gene of Escherichia coli K-12, we show that levels of DNA adenine methylase activity are correlated with the spontaneous mutation frequency.
Subject(s)
Bacterial Proteins/genetics , Escherichia coli/genetics , Methyltransferases/genetics , Mutation , Bacterial Proteins/physiology , DNA Repair , DNA, Bacterial/metabolism , Methyltransferases/physiology , Plasmids , Site-Specific DNA-Methyltransferase (Adenine-Specific)ABSTRACT
2-Aminopurine induces damage inducible (SOS) repair in an Escherichia coli dam-4 strain but not in a dam-4 mutS456 derivative or in dam+ bacteria.
Subject(s)
2-Aminopurine/pharmacology , Adenine/analogs & derivatives , DNA Repair/drug effects , Escherichia coli/drug effects , Methyltransferases/genetics , DNA (Cytosine-5-)-Methyltransferases/physiology , DNA, Bacterial/metabolism , Enzyme Induction , Escherichia coli/genetics , Site-Specific DNA-Methyltransferase (Adenine-Specific)ABSTRACT
A recombinant plasmid, pMQ3, carrying the dam gene of Escherichia coli K-12, was constructed and transformed into dam+ and dam- strains. Both dam- and dam+ strains containing pMQ3 showed a wild phenotype for all traits, including mutation rate, except for a 10-fold increase in DNA adenine methylase activity.
Subject(s)
DNA (Cytosine-5-)-Methyltransferases/genetics , Escherichia coli/genetics , Genes, Bacterial , Methyltransferases/genetics , Transformation, Bacterial , Cloning, Molecular , DNA, Recombinant , Escherichia coli/enzymology , Mutation , Phenotype , Plasmids , Site-Specific DNA-Methyltransferase (Adenine-Specific)ABSTRACT
The dam gene of E. coli can be inactivated by insertion of Tn9 or Mud phage. Strains bearing these mutations are viable indicating that the dam gene product is dispensable.
Subject(s)
Escherichia coli/genetics , Genes, Bacterial , Methyltransferases/genetics , DNA Transposable Elements , Mutation , Site-Specific DNA-Methyltransferase (Adenine-Specific)ABSTRACT
The ebg beta-galactosidase of Escherichia coli K-12 strain LC110 has been purified and characterized. Strain LC110 is a Lac+ revertant of a mutant with a deletion of the lacZ beta-galactosidase gene. Its new ebg beta-galactosidase activity was shown to be due to a discrete protein, immunologically unrelated to lacZ beta-galactosidase. Its kinetics of action conformed to those of a simple conventional enzyme. With o-nitrophenyl-beta-D-galactoside as substrate, the Vmax was 11,200 nmol/min per mg of enzyme, the Km was 5 mM, and the activation energy was 12,400 cal/mol. Corresponding values for lacZ beta-galactosidase of wild-type E. coli K-12 were 350,000 nmol/min per mg of enzyme, 1.3 mM, and 8,000 cal/mol. A series of sugars has been examined as competitive inhibitors of ebg beta-galactosidase. Kinetic analyses suggest that ebg beta-galactosidase has a particularly high affinity for galactosamine and gamma-galactonolactone, binds galatose more tightly than lactose, and shows a general preference for monosaccharides rather than beta-galactosides. We conclude that the ebg beta-galactosidase may have arisen by modification of a gene involved with the metabolism of a monosaccharide, possibly a 2-amino sugar.
