Recombination in bacteriophage lambda. I. Mutants deficient in general recombination

Fate of transforming DNA after uptake by competent Bacillus subtilis: failure of donor DNA to replicate in a recombination-deficient recipient

The fate of radioactively-labeled transforming DNA was studied in a recombination-deficient strain of Bacillus subtilis that carried the recB2 mutation (Rec(-)) and was sensitive to radiation. Experiments performed with extracts of this strain after transformation showed that the recovery of donor transforming activity and the appearance of recombinant transforming activity occurred to the same extent as in the Rec(+) strain. Sucrose gradient analyses revealed that donor-recipient complex is also formed to the same extent in the Rec(-) and Rec(+) strains, but that 80-90% of the donor genetic material in the complex failed to replicate in the Rec(-) mutant.

Mutation and recombination of bacteriophage lambda: effect of ultraviolet radiation

Defects in the bacterial recB or recC or phage red or int gene did not impair ultraviolet light-induced clear mutations of lambda phage. Clear mutants of cI and cII genes were not enriched among RecA-promoted UV-induced recombinants between the N and O genes which closely encompass the c genes. No correlation was observed between UV-induced mutation and genetic recombination.

Heat-sensitive early function in induced lambda Nsus lysogens

Mutations in gene N of lambda prevent killing of the host bacterium after infection. However, derepression of Nsus prophages in nonpermissive (pm(-)) bacteria results in death of the lysogens. When prophages in pm(-)(lambdaCItsA-Nsus) lysogens are derepressed by raising the temperature to 45 C, the cells remain viable as long as they are at 45 C. However, they cannot form colonies at 33 C unless they have been superinfected, at the high temperature, by lambdaCI(+)-Nsus phage which produces repressor at 45 C. A large fraction of these "rescued," heat-inducible lysogens are lysogenized by the superinfecting phage, but lysogenization is not required for rescue. In pm(-)(lambdaCItsA-Nsus) lysogens growing at 45 C, the rate of deoxyribonucleic acid (DNA) synthesis shows a characteristic increase after the temperature is lowered. This increased DNA synthesis, which is correlated with loss of rescue potential, does not occur as long as the cultures are maintained at 45 C.

An ATP-dependent deoxyribonuclease from Escherichia coli with a possible role in genetic recombination

A DNase which requires ATP for its function was purified from E. coli and some of the characteristics of the purified enzyme were studied. This enzyme activity could not be detected in certain (recB and recC) recombination deficient mutant strains. The possible role of the enzyme in genetic recombination is discussed.