Abstract
When a λC I + bacteriophage infects a lysogenic bacterium containing a heat-in -ducible λ prophage, the lysogen becomes heat resistant. Heat resistance is taken to indicate the presence of a heat-stable product of the C I + gene. Some bacteria of a heat-sensitive culture are heat resistant 3 minutes after the addition of a C I + phage. Twelve minutes after superinfection, most of the superinfected bacteria are heat resistant. Heat-inducible lysogens superinfected with λC I + segregate progeny that are not induced at 43 ° although they no longer contain the C I + gene. The persistence of heat resistance in lysogens several generations removed from the superinfected cell suggests that the λC I + product is a stable substance. A single superinfecting λ + genome can prevent heat induction of a lysogen that contains several heat-inducible prophages. It is proposed that the substance that prevents induction of λ is an oligomer of several molecules of C I product. One or more heat-stable subunits are assumed to prevent heat inactivation of an oligomer containing one or more subunits of heat-labile C I product.
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