Heterochromatin is defined as tightly packed form of DNA. But some experiments show that the average spacing of nucleosomes associated with H3K9me3 and H3K27me3, both heterochromatin marks, are longer than those with euchromatin marks. why packed DNA has longer spacing?
e.g in article :Genome-Wide Nucleosome Positioning Is Orchestrated by Genomic Regions Associated with DNase I Hypersensitivity in Rice. it says:"The average spacing of nucleosomes associated with H3K4me1 and H3K27ac, both euchromatin marks, are 178 bp and 179 bp, respectively. In contrast, the average spacing of nucleosomes associated with H3K9me3 and H3K27me3, both heterochromatin marks, are 205 bp"
