Nucleosome spacing in rat liver chromatin. A study with exonuclease III.

Exonuclease III was used to uniformly trim DNA ends of micrococcal nuclease-prepared chromatin fragments down to the first major impediment encountered by the enzyme, which arises from the interaction of H1 with the nucleosome. This trimming, when performed on nucleosome dimers, allowed one to quantitatively determine the center-to-center distance of nucleosomes. This distance, of mean 198 base pairs, was found to essentially vary between about 180 and 215 base pairs, with extremes of 165 and 230 base pairs. Trimming of trimers further revealed that the overall arrangement of nucleosome center-to-center distances along the chromatin fiber is that expected on a statistical basis.