Positioning of nucleosomes in satellite I-containing chromatin of rat liver.

The location of nucleosomes on rat satellite I DNA has been investigated using a new approach. Nucleosome cores were prepared from rat liver nuclei with micrococcal nuclease, exonuclease III and nucleases S1. From the total population of core DNA fragments the satellite-containing fragments were isolated by molecular cloning and the complete sequence of 50 clones was determined. The location of nucleosomes along the satellite sequence was found to be non-random. Our results show that nucleosomes occupy a number of positions on satellite I DNA. About 35 to 50% of all nucleosomes are positioned in two corresponding major sites, the remainder in about 16 less preferred sites. The major nucleosome positions are apparently strictly defined with the precision of a single base-pair. These results were confirmed by other approaches, including restriction nuclease digestion experiments. There are good indications of a defined long-range organization of the satellite chromatin fiber in two or more oligonucleosomal arrays with distinct nucleosome configurations.