Chromosome regions enriched in hyperacetylated histone H4 are preferred sites for endonuclease- and radiation-induced breakpoints

Previously, we have shown that breakpoints induced by the endonucleases Alu I, BamHI and DNase I in CHO chromosomes are localized mainly in G-light ban ds. Neutrons and gamma rays produced similar breakpoint clusters to endonuc leases in most CHO chromosomes. Here we compare endonuclease- and radiation -induced breakpoint maps with hyperacetylation patterns of histone H4. The H4 acetylation pattern in chromosomes is similar to the pattern of G-light, or R-bands, and breakpoints are clustered in highly acetylated chromosome regions. These findings indicate that chromosomal aberrations occur more fr equently in active than in inactive chromatin.