Integration and Induction of Phage P22 in a Recombination-deficient Mutant of Salmonella typhimurium

摘要

Phage P22 can integrate as prophage into a recombination-deficient (Rec?) strain of Salmonella typhimurium. At 37 C, the integration efficiency is only 10% that in Rec+ infection, but at 25 C the efficiencies in Rec? and Rec+ hosts are similar. Rec? lysogens cannot be induced by ultraviolet irradiation or by treatments with the chemical inducing agents streptonigrin or mitomycin C. Heat induction of Rec? cells lysogenic for a temperature-sensitive c₂ mutant (ts c₂) is normal, showing that the Rec? cell has the machinery necessary for prophage excision. Ultraviolet irradiation of Rec? (ts c₂) lysogens prior to heat induction does not prevent the formation of infective centers after temperature shift. Thus, the noninducibility of Rec? lysogens is not due to destruction of the prophage as a result of ultraviolet irradiation. Deoxyribonucleic acid-ribonucleic acid (RNA) hybridization experiments demonstrate that no increase in phage-specific RNA synthesis occurs after ultraviolet irradiation of a Rec? (c+) lysogen. The Rec? mutant appears to lack part of the mechanism required to destroy the phage repressor and allow the initiation of early phage functions such as messenger RNA synthesis. A similar conclusion was reached previously for an Escherichia coli Rec? strain.