Electron microscopic and biochemical analyses of the organization of human sperm chromatin decondensed with sarkosyl and dithiothreitol.

Human sperm chromatin was decondensed by treating the purified sperm heads with Sarkosyl for 60 minutes followed with dithiothreitol (DTT) for 20 minutes and overnight. Following Sarkosyl treatment all histones and nonhistones were removed; the remaining nucleoprotamines in the sperm heads exhibited two levels of higher-order structure in the forms of 900-1200 A thick and 380-520 A thin knobby cords, which were randomly coiled. Subsequent treatment with DTT resulted in the dissociation of the 380-520 A cords into subunits of 180-210 A fibers, which were further decondensed into beads-on-a-string structure with diameter of the beads about 120-150 A.