Control of development in temperate bacteriophages. I. Induction of prophage genes following hetero-immune super-infection

Defective mutants from several cistrons of bacteriophage λ give a normal or subnormal burst following infection of a bacterial strain lysogenic for a closely related but hetero-immune bacteriophage, whereas there is no phage production on the corresponding, non-lysogenic, strain. This effect ("prophage complementation") results from the induction of prophage genes following the heteroimmune super-infection. Since the control exerted by immunity on these genes can thus be by-passed in trans, one has to conclude that these genes are not directly blocked by immunity; rather, the immunity repressor prevents the synthesis of a diffusible substance which normally operates as an inducer of these genes. The results suggest that gene N has the key role of producing the early inducer. The immunity represser prevents N from operating and thence indirectly blocks the other functions. From a more general viewpoint, the situation described here offers concrete examples of the mechanisms which may be involved in the orderly expression of a developmental process. The occurrence of triggering of groups of genes by diffusible products originating from "earlier" genes deserves special mention. © 1966.SCOPUS: ar.j