(1) accommodate larger DNA inserts and
(2) to ensure that the recombinant phage is always lytic.
Several vectors were produced from wild type λ genome by mutation and recombination in vivo as well as by recombinant DNA techniques. These vectors have the following two basic features.
(1) The vector itself can be propagated as phage in E. coli cells enabling preparation of vector DNA.
(2) They contain restriction sites, which allow the removal of the lysogenic segment and also provide insertion site for the DNA fragment.
During annealing and ligation of the DNA insert with the λ vector, two or more recombinant DNAs may join end-to-end producing a concatemer, which is the proper precursor for packaging of λ genome into phage heads.
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