Novel mutants of Escherichia coli that produce recombinogenic lesions in DNA : II. Properties of recombinogenic λ phages grown on bacteria carrying arl mutations

Abstract

Lambda duplication phages grown for several rounds on Escherichia coli strains containing arl mutations were recombined at elevated frequencies (3 to 6-fold higher) in subsequent test infections. Enhanced recombination of Arl − phages (grown on arl bacteria) was demonstrable by assays for altered genetic linkages as well as by the standard assay, which measures the conversion of duplication phages (EDTA-sensitive) to single-copy phages (EDTA-resistant). The accumulated potential for enhanced recombination was lost during subsequent growth of the phages on arl + bacteria. Arl − phages had the same mutation frequencies, at a variety of loci, as control phages; arl bacteria themselves exhibited normal mutation rates. Arl − phages had normal plating efficiencies and buoyant densities. DNA extracted from Arl − phages exhibited the same frequency of strand interruption, the same superhelical density (when circularized in vivo), and the same thermal denaturation profile as DNA from phages grown on arl + bacteria. Recombination of Arl − phages in the presence of λ repressor was very low, as is the case for normal phages. The recombination frequency of ultraviolet light irradiated (80 J/m 2) Arl − phages was more than twice the sum of the frequencies for unirradiated Arl − phages and irradiated control phages. Substantially increased recombination of Arl − phages was observed when either the E. coli RecBC, or RecE (but not RecF) pathway was active.