Bacterial genetic factors controlling the suppression of T4 phage Amber mutants

Summary

Recombinant bacteria issuing from crosses between Hfr and F ⁻ E. coli strains which differ in their amber and “non-amber-suppressor sensitive” phage mutant suppression patterns exhibit the two parental phage suppression patterns and five other patterns. Analysis of the suppression patterns and comparisons of the chromosomal marker frequencies among the seven different recombinant classes permit identification of five distinct chromosomal regions which are sites of suppressor genes for which the parental strains carry different alleles: 1. the str region of the Hfr chromosome, 2. the (λ)-gal region of the F ⁻ chromosome, 3. the met-xyl region of the F ⁻ chromosome, 4. the thr region of the Hfr chromosome, and 5. the his-try region of the Hfr chromosome.

The suppressor in the str region is probably coincident with the gene(s) determining the str phenotype of the parental Hfr strains. The suppressor residing in the (λ)-gal region of the F ⁻ chromosome appears to be the su _II glutamine-inserting suppressor. The quantitative expression of su _II appears to be reduced by the presence of the Str^r mutation carried by the F ⁻ parent, and this reduced efficiency of suppression can be counteracted progressively by the presence of the suppressor residing in the met-xyl region of the F ⁻ chromosome and of the two suppressors residing in the thr and his-try regions of the Hfr chromosome.