Mutual exclusion between related phages

The discovery of the breakdown of superinfecting phage needs to be supplemented by genetic tests to find out whether the phage whose nucleic acid is broken down is, indeed, unable to contribute genetic markers to the progeny. The present paper presents experiments of this kind, whose results leave no doubt that the breakdown of superinfecting phage is strictly paralleled by exclusion from the progeny of the genetic markers it contains. We are presenting also some experiments in which the stimulating phage alone or both the stimulating and the superinfecting phage have been inactivated by irradiation with ultraviolet light. These experiments serve to characterize functions which have remained unimpaired in ultraviolet treated phage and their relation to multiplicity reactivation of ultraviolet treated phage