Studies on polylysogens containing λN^-cl^- prophages I. Control of synthesis and maintenance of a large number of integrated λ genomes

Abstract

Study of the control of λ DNA synthesis in polylysogens containing 20-25 copies of integrated λN^-cl^- prophages per bacterial genome shows that in absence of the functional products of O and P genes, only 7-8 copies per host genome are maintained. Introduction of constitutive mutations v1v3 in the right operator increases the prophage genome copies to 52. In a mixed polylysogen containing both λN^-cl^- and λ imm434N^-cI^- prophages, the total number of phage genomes is also increased to 50. The levels of cro activity in all the polylysogens of λ vary almost proportionately with of the number of prophages. All these results indicate that the maintenance of 20-25 copies of integrated phage genome in λN^-cl^- polylysogens is the result of both passive and O and P protein-mediated synthesis, and that the latter may be regulated by the cro gene product.