Heat-Sensitive Early Function in Induced λ N sus Lysogens

Abstract

Mutations in gene N of λ prevent killing of the host bacterium after infection. However, derepression of N sus prophages in nonpermissive (pm − ) bacteria results in death of the lysogens. When prophages in pm − (λCI ts A-N sus ) lysogens are derepressed by raising the temperature to 45 C, the cells remain viable as long as they are at 45 C. However, they cannot form colonies at 33 C unless they have been superinfected, at the high temperature, by λCI + -N sus phage which produces repressor at 45 C. A large fraction of these “rescued,” heat-inducible lysogens are lysogenized by the superinfecting phage, but lysogenization is not required for rescue. In pm − (λCI ts A-N sus ) lysogens growing at 45 C, the rate of deoxyribonucleic acid (DNA) synthesis shows a characteristic increase after the temperature is lowered. This increased DNA synthesis, which is correlated with loss of rescue potential, does not occur as long as the cultures are maintained at 45 C.