Histone hyperacetylation is accompanied by changes in DNA topology in vivo

The effect of histone acetylation on the topology of plasmids transfected into COS7 cells was examined. Parallel determinations of histone profiles and DNA topology showed that with increasing levels of acetylation the minichromosomal DNA is gradually relaxed. This effect could not be attributed to the increased transcriptional activity accompanying butyrate treatment since plasmids with different promoter strengths exhibited similar superhelical densities. Considering that the number of nucleosomes/minichromosome were constant under these conditions, the data suggest that in vivo histone hyperacetylation reduces the linking number change/nucleosome.