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The Relation between Breakdown of Superinfecting Virus Deoxyribonucleic Acid and Temporal Exclusion Induced by T4 and T5 Bacteriophages

Microbiology Unit, Department of Biochemistry, South Parks Road, Oxford

Temporal exclusion and breakdown of superinfecting virus deoxyribonucleic acid were measured after infection with T4 and T5 bacteriophages of normal strains of Escherichia coli and strains deficient in endonuclease-I. Bacteria deficient in endonuclease-I when infected with T4 phage excluded superinfecting T4 with little solubilization of the secondary DNA. With wild-type bacteria exclusion was accompanied by extensive superinfection breakdown, probably caused by the bacterial endonuclease-I. In bacteria infected by T5 phage, superinfecting T2 phages could be excluded even when deoxyribonucleic acid degradation was inhibited by maintaining a low [Mg²⁺] in the growth medium. In the presence of 0.01 M-magnesium ions, both wild-type bacteria and bacteria deficient in endonuclease-I infected with T5 phage produced extensive solubilization of the DNA of superinfecting T2 or T4 phages. A nuclease induced by T5 was probably partly responsible for the DNA breakdown which occurred in these conditions.

Received 12 August 1969; accepted 20 October 1969.