Mapping of a human centromere onto the DNA by topoisomerase II cleavage

We have mapped the positions of topoisomerase II binding sites at the centr omere of the human Y chromosome using etoposide-mediated DNA cleavage. A si ngle region of cleavage is seen at normal centromeres, spanning similar to 50 kb within the centromeric alphoid array, but this pattern is abolished a t two inactive centromeres. It therefore provides a marker for the position of the active centromere. Although the underlying centromeric DNA structur e is variable, the position of the centromere measured in this way is fixed relative to the Yp edge of the array, and has retained the same position f or >100 000 years.