Changes in the higher order organization of DNA during aging of human fibroblast-like cells

Nucleosome spacing (DNA repeat length) was determined in human diploid fibroblast-like cells (HDF) of different in vitro ages following the electrophoretic separation of micrococcal nuclease digestion products. The results indicate that a heterogeneity of DNA repeat lengths is present in HDF of all in vitro ages. In older cells the organization of part of the DNA is conserved, but a greater proportion of shorter repeats is evident. The shorter repeat lengths are not due to nucleosome sliding, but result from the presence of shorter linker regions which are reduced by as much as 25% in part of the chromatin of high PDL cells.