Interference in Bacteriophage Growth by a Resident Plasmid λdv II. Role of the Promoter-Operator

Abstract

The susceptibilities to interference by λdv of a set of λ phages differing in the genetic structure of their right promoter-operator (pRoR) were compared. For this purpose mutant phages were added to λdv-carrier cells at various multiplicities, and abilities to escape from interference, as represented by percentages of infected complexes to produce progeny phages, were compared. It was observed that phages that carry strongly constitutive pRoR were able to escape from interference at a low multiplicity of infection, whereas phages with weakly constitutive pRoR were able to escape only when a large number of these genomes entered into a cell. Several mutations in the pRoR were arranged in order of their constitutivity, or ability to escape from interference. Next, the abilities of a set of λdv plasmids differing in their pRoR to cause interference were compared. The results showed that interference increased with increase in constitutivity of the pRoR in the plasmid genome. These observations are thought to reflect a regulatory system of the plasmid replicon, and a possible mechanism for the system is discussed.