In contrast, the recombinant vectors produce colourless plaques, which are readily identified. A 42 bp poly linker sequence having several unique restriction sites is so placed within the lacZα that it allows the production of amino terminal portion of the enzyme β-galactosidase.
However, when a DNA insert is placed anywhere within the polylinker sequence the formation of amino terminal part of the enzyme is prevented. It may be pointed out that the pUC series of plasmid vectors also employ a similarly placed poly linker sequence.
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