Abstract
When a λ-lysogenic recombination-deficient (rec-) mutant of Escherichia coli K12, AB 2463 (λ), was superinfected with ultraviolet-irradiated λ in the presence of 6-azauracil, there was found among surviving cells a doubly lysogenic form, AB 2463 (λ)(ind), with rec+ phenotype. The double lysogen obtained by superinfection of AB 2463 (λ) with λcI 857 ind- displayed a rec- phenotype at 30° and rec+ characteristics at 40°. Superinfection of AB 2463 (λ) with phage 434hy 2c+h, which lacks the c region of λ, yielded rec- double lysogens. Since heat inactivation of the repressor in AB 2463 (λ) (λcI 857 ind-) produced a rec+ form one of the prophages in AB 2463 (λ)(ind) may have been incompletely repressed, hence the expression of its recombination function. For its host-converting effect the superinfecting phage appeared to require the c region of its genome. The results of recombination analysis suggested that in AB 2463 (λ)(ind) the first prophage was integrated normally while the second prophage occupied a tandem position more distant than usual, and/or existed in a special relationship conferring on it immunity from or the capacity to overcome the repressor function of the cI product in respect of gene recombination function.
* Present address: New Zealand Dairy Research Institute, P.O. Box 1204, Palmerston North, New Zealand.