Evidence for a New Endonuclease Synthesized by λ Bacteriophage

Abstract

Infection of nonlysogenic Escherichia coli CR34(S) (Thy ⁻ ) with bacteriophage λ C _I 857 resulted in the formation of twisted circular double-stranded phage deoxyribonucleic acid (DNA; species I). When such infected bacteria were incubated in the absence of thymine, there was a significant decrease in the amount of species I DNA after 60 min of incubation. A similar loss of species I λ DNA during incubation in a thymine-deficient medium was also observed after infection of the endonuclease I-deficient strain, E. coli 1100(S) (Thy ⁻ ). This destruction of twisted, circular λ DNA in thymine-deprived cells did not occur in the presence of chloramphenicol nor in lysogenic E. coli CR34 carrying a noninducible λ prophage. It is therefore concluded that the endonuclease which attacks this circular configuration of λ DNA is newly synthesized after infection and is directed by the phage chromosome.