Chapter 9 Lambda DNA Replication

Abstract

There are two modes of replication of λ DNA. As prophage incorporated into the DNA of its host, λ DNA is passively replicated along with the other elements of the bacterial chromosome. Under these conditions phage functions would interfere with bacterial functions, and the c I gene of the phage works in a specific way to repress phage functions. The prophage is replicated once in each bacterial generation. Prophage replication itself requires no help from λ genes. When a susceptible bacterium is infected by λ under conditions favoring multiplication as opposed to lysogenization, a different train of events is set in motion. Lambda DNA starts to replicate independently of the bacterial DNA and it generates about one hundred replicas in a time equivalent to one bacterial generation. This autonomous replication depends on proteins coded in genes O and P and on a specific site in the DNA at which a cycle of replication begins. In one infectious cycle λ DNA passes through a series of different forms. As isolated, and as far as is known, these forms consist entirely of phage DNA; they contain no host DNA. During the first half of the latent period, λ DNA replicates as a circle and generates circles. During the second half of the latent period, from a replicative intermediate of as yet undefined structure, the characteristic linear molecules found in phage particles are produced. CIRCULAR DNA STRUCTURES When a particle of phage λ infects a bacterium, it injects a linear DNA molecule into its...