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Index >> Bacteriophages - Part Two >> Late Replication in Lambda Phage

Late Replication in Lambda Phage

	Late Replication in Lambda Phage - In late replication the progeny DNA molecules leave the cell membrane and switch over from the bidirectional to the rolling circle mode of replication. Initiation occurs at variable points on the cyclic DNA molecule. Multiple unit length DNA duplexes called, concatemers are generated.
Recombination can also take place, producing oligomers of lambda DNA. Concatemeric DNA is cut up into unit length pieces, resulting in the formation of mature molecules with cohesive ends. The cuts are made by phage gene A protein. This binds to the concatemers at sites corresponding to the cohesive ends (cos) , and produces staggered single-stranded cuts 12 nucleotides apart. The sticky ends are thus regenerated.
The unit-length duplex produced contains exactly one phage genome. Control of transformation from early to late replication depends on phage genes under the control of the N gene. DNA molecules with defective N replicate continuously in cyclic form, without undergoing rolling circle replication. The function of the viral gene gam is required to inhibit the recBC endonuclease V of the host, which would otherwise break down the concatemers.

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