Repression of λ-Associated Enzyme Synthesis After λ vir Superinfection of Lysogenic Hosts

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Abstract
Lisio, Arnold L. (National Institutes of Health, Bethesda, Md.), and Arthur Weissbach. Repression of λ-associated enzyme synthesis after λvir superinfection of lysogenic hosts. J. Bacteriol. 90:661–666. 1965.—Phage λvir is a multiple mutant of λ which is capable of overcoming the immunity of a host lysogenic for λ, and initiating normal vegetative replication of the superinfecting phage genome. Superinfection of Escherichia coli K-112 (λ22) with λvir results in a normal phage yield, lysis time, and H3-thymine incorporation compared with infection of the sensitive host, K-112 (S). However, the production of the λ phage-specific early protein, λ-exonuclease, after superinfection of E. coli K-112 (λ22) with λvir is only 25 to 50% of that obtained from corresponding infection of a nonlysogenic host, E. coli K-112 (S). This repression of λ-exonuclease synthesis is dependent on the C1 cistron of the prophage and is overcome if the lysogenic host cells are induced prior to superinfection. The data are interpreted as evidence for partial repression of λvir by the host immunity.