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The Genetics of the Anti-immune Phenotype of Defective Lambda Lysogens

E. Calef, A. Avitabile, L. Del Giudice, C. Marchelli, T. Menna, Z. Neubauer, A. Soller


Heat inducible λ lysogens surviving induction carry two prophage mutations: one in gene N, the other in x, zd, O, or P. The lysogens carrying the defective prophage Nzd, NO or NP can exist in two distinct physiological states: immune (im+ phase) and anti-immune (im phase). The im+ phase is characterized by the presence of immunity against the homoimmune superinfecting phage and repression of early phage functions. The im phase is characterized by the absence of immunity, derepression of the xO operon, and channeling of the superinfecting homoimmune phage towards the lytic cycle. When the prophage contains a mutation in x, the xO operon cannot be transcribed and the im phase cannot be established (Neubauer and Calef, 1970).

The im+ and im phases are hereditary for the whole line of cells. However, the cell populations always contain 0.1–1% of cells which give rise to colonies of the opposite phase. This phenomenon, called the “immunity phase shift,” is of a nonmutational character; when such temperature sensitive defective lysogens are deprived of immunity by heat, the whole im+ population shifts to the im phase.

From these results the following conclusions were possible: (a) The two prophage mutations are sufficient to allow the bacteria to survive the absence of immunity. (b) The presence of an immunity specific cytoplasmic factor, called anti-immunity, antagonizes the establishment of immunity in the im phase.

Starting from these points and aiming towards a definition of the genetics of the novel anti-immune phenotype we tried...

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