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J Virol. 1968 October; 2(10): 1096-1101
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Evidence for a New Endonuclease Synthesized by Bacteriophage

^a National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014

ABSTRACT

Infection of nonlysogenic Escherichia coli CR34(S) (Thy^–) with bacteriophage C_I857 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 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 DNA in thymine-deprived cells did not occur in the presence of chloramphenicol nor in lysogenic E. coli CR34 carrying a noninducible prophage. It is therefore concluded that the endonuclease which attacks this circular configuration of DNA is newly synthesized after infection and is directed by the phage chromosome.

¹ Present address: Department of Biochemistry, Emory University, Atlanta, Ga., 30322.

² Visiting Scientist, Roche Institute of Molecular Biology.