Distinctive higher-order chromatin structure at mammalian centromeres

The structure of the higher-order chromatin fiber has not been defined in d etail. We have used a novel approach based on sucrose gradient centrifugati on to compare the conformation of centromeric satellite DNA-containing high er-order chromatin fibers with bulk chromatin fibers obtained from the same mouse fibroblast cells. Our data show that chromatin fibers derived from t he centromeric domain of a chromosome exist in a more condensed structure t han bulk chromatin whereas pericentromeric chromatin fibers have an interme diate conformation. From the standpoint of current models, our data are int erpreted to suggest that satellite chromatin adopts a regular helical confo rmation compatible with the canonical 30-nm chromatin fiber whereas bulk ch romatin fibers appear less regularly folded and are perhaps intermittently interrupted by deformations. This distinctive conformation of the higher-or der chromatin fiber in the centromeric domain of the mammalian chromosome c ould play a role in the formation of heterochromatin and in the determinati on of centromere identity.