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The Restriction of Bacteriophage in Escherichia coli Strain w

J. Aronovitch

Medical Research Council, Microbial Genetics Research Unit, Hammersmith Hospital, Ducane Road, London, W. 12.

Escherichia coli strain W adsorbs phage very efficiently but the phage does not form plaques on this strain. In a very small fraction (10^-4) of the infected cells the phage grows and produces small bursts of progeny phage also unable to form plaques on strain W. E. coli strain W is lysogenic for a temperate phage, W, related to phage P2. Non-restricting hosts for phage became restricting hosts when made lysogenic for W. When ³²P-labelled adsorbed to restricting W lysogenic hosts, > 20% of the ³²P become acid-soluble shortly after infection. No W specific modification was carried by the small number of phages which escaped this restriction process. It is concluded that W controls a host-restriction mechanism but not a host-modification process, and in parallel with other examples of host-controlled restriction and modification can be represented as r⁺m^- or r⁺m°. W mutants have been isolated which escape this restriction and which form plaques on strain W and W lysogenic strains with an efficiency of 1.0. With these mutants a W-specific host modification controlled by the genome of strain W was demonstrated. Mixed infection experiments with restricted and unrestricted W showed that that restricted phage did not block the growth of the unrestricted mutant nor did the mutant permit the restricted phage to grow. In addition it was shown that obtained from bacteria mixedly infected with and w was still unable to grow in restricting hosts and w similarly obtained from mixedly infected bacteria still retained its ability to grow on restricting hosts. It is concluded that there is a nucleotide sequence in the DNA of phage which, when infects a restricting host, is specifically recognized by the restriction mechanism controlled by the W. The mutation to w involves an alteration to this sequence such that it is no longer recognized by the restriction mechanism of the W.

Mutants of W were isolated not restrictive for phage .

^* Permanent address: Department of Microbiology, University of Lodz, Nowotki 18, Lodz, Poland.

Permanent address: Department of Bacteriology, Hadassah Medical School, The Hebrew University, Jerusalem, Israel.

Received 28 January 1967; accepted 15 March 1967.

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