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Chapter 9 Lambda DNA Replication

Dale Kaiser


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 cI 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.

When a particle of phage λ infects a bacterium, it injects a linear DNA molecule into its...

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