
Full text loading...
In a culture of Escherichia coli K12 gal (γdg), cells which form large colonies on agar plates containing galactose and thiomethyl β-d-galactoside (TMG) appear at high frequency. These clones are resistant to growth inhibition by TMG on galactose minimal medium. Biochemical studies of the steady-state levels of galactokinase and UDPgalactose 4-epimerase suggest that the resistant clones have extra copies of the genes for the galactose-metabolizing enzymes. The mutation for TMG resistance is not located in either the bacterial or the bacteriophage genome, but is probably due to an aberrant association between cell and prophage DNA.
Mapping the TMG-resistant characteristic by phage P1 indicates that TMG-resistant bacteria possess at least two gal + operons, one of which is cotransducible with bio +. In addition, TMG-resistant bacteria behave like λdg polylysogens when challenged with the phage λcI90c17. From these genetic experiments we conclude that TMG-resistant bacteria arise by duplication of the λ dg prophage. Finally, gal + bacteria which carry a single, additional, λ dg prophage are TMG-resistant. TMG resistance is probably a gal + gene dosage effect.
Article metrics loading...
Full text loading...
References
Data & Media loading...