Fast electrophoresis in superposed agarose minigels for DNA topoisomerase assays

Superposed miniature agarose slab gels and relatively small plasmids were used to evaluate the DNA topoisomerase I activity associated with the chromatin of normal human fibroblasts at three different in vitro population doubling levels. Results obtained in a short period of time with a single miniature electrophoresis unit confirm an increase in DNA‐relaxing enzyme activity with cell age.