Studies on chromatin. IV. Evidence for a toroidal shape of chromatin subunits

Abstract

Electron microscopy of purified chromatin subunits (ν-bodies [17] or nucleosomes [2] revealed a hole or at least a deep indentation in the globular nucleosome. A hole in the nucleosome was visualized using rotatory shadowing with platinum-palladium or more directly, by negative staining with sodium phosphotungstate. The diameter of the hole as measured from negatively stained samples is 10–25Å. The external diameter of the negatively stained nucleosome equals 75±15Å. Although most of the data are formally compatible with either a hole or a deep indentation in the nucleosome, some views of the particles in the negatively stained samples suggest a hole rather than an indentation. The possible significance of a toroidal structure of the chromatin subunit is discussed in the accompanying paper [3].

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