Role of bacteriophage DNA replication in λ dg escape synthesis

Abstract

The vegetative development of a bacteriophage carrying a repressible bacterial operon in its genome is accompanied by a large increase in the rate of synthesis of the gene products specified by the operon (“escape synthesis”). We have used λ dg phage carrying mutations in essential phage genes to determine which phage functions are necessary for the gal operon to escape repression; these experiments show that the λ dg must be able to carry out DNA replication. To clarify the role of phage DNA replication, we have shown that it is not necessary for a bacterial operon to be physically associated with a replicating phage in order for escape synthesis to occur; the gal operon of the host chromosome is also derepressed during λ dg replication. These findings strongly support an explanation for gal escape synthesis in which derepression results from a depletion of free repressor supply by the presence of the many gal operator regions provided by a replicating λ dg.