Genetics and physiology of defective lysogeny in K12 (λ): Studies of early mutants

The properties of a number of strains of K12 (λ) which are defective in their ability to form lambda DNA after induction have been examined by genetic, physiological, and biochemical tests. The strains fall into four classes, and include mutants in cistrons N, O, and P, previously identified by Campbell (1961), and a fourth new class, called x, in a region between CI and CII. Mutants in each of the classes can be distinguished genetically, by their relative ability to form the λ-exonuclease, and by their tendency to show curing of their prophage after induction. Mutants in the P and O cistrons form normal levels of λ-exonuclease, whereas mutants in the N cistron form very low levels, and mutants in the x region, relatively high levels of this enzyme. Curing is very efficient for mutants in the x region, less efficient for mutants in the O and P cistrons, and is seldom observed with mutants in the N cistron. These patterns of curing are reflected in the curves for UV survival of the strains carrying defective mutations in the various cistrons. The significance of these findings in respect to the early events in phage development are discussed. © 1966.SCOPUS: ar.j