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Cloning-qualified blunt end restriction enzymes: Causes and cures for light blue
colonies
Elizabeth Murray, Karen Singer, Karen Cash and Ray Williams
Promega Corporation
Using a blue/white cloning assay, we have identified a novel contaminant in blunt
end restriction enzymes. This contaminant removes a single base from the 3´ end of the
restriction enzyme recognition sequence and results in light blue false positive colonies
upon religation. We have purified this contaminant away from Promega's blue/white
cloning-qualified blunt end restriction enzymes. In performance comparisons of Sma
I, Hinc II, EcoR V and EcoICR I, each of four other vendors supplied
one or more enzyme lot which failed to meet Promega's blue/white assay specification.
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