Protection of DNA during preparative agarose gel electrophoresis against damage induced by ultraviolet light

Preparative gel electrophoresis of double-stranded DNA usually includes staining the gel with ethidium bromide followed by illumination with ultraviolet (UV-B) light. In this report, DNA isolated from agarose gels was found to be a poor substrate for in vitro transcription, transformation of E. coli and PCR. Inhibition was not caused by enzyme-inhibiting impurities in the agarose gel, but was induced by a standard transilluminator fitted with 312-nm tubes. Interestingly, it was possible to protect the DNA against UV damage by the addition of cytidine or guanosine to the electrophoresis buffer.