Cytochemical, radioautographic, and microspectrophotometric studies bearing on the relationship of histone transition to the origin and development of the protein and RNA components of the "sphère chromatophile" in the developing spermatogenic cells of the albino rat are presented. These studies show that the sphère chromatophile has many features in common with somatic nuclei: it contains histonelike basic proteins rich in lysine, with lesser amounts of arginine. No evidence is found for the presence of a protamine in this granule. The sphère chromatophile is rich in RNA, but contains no DNA. The failure of a positive reaction with basic protein stains, unless the RNA is first removed, indicates either a chemical bonding or a very close association between the RNA and basic protein. The basic protein and RNA components of the sphère chromatophile appear to have different origins in the cell. A sequence of stages in the development of the lysine-rich basic protein component of this structure commences with the appearance of tiny grains in those spermatid nuclei which are beginning to replace lysine-rich histones with arginine-rich histones. Subsequently, similar-staining cytoplasmic grains appear, which coalesce to form the sphère chromatophile in the cytoplasm. Labeling studies show that the basic protein component is synthesized at about the time of the last premeiotic DNA (and histone) synthesis. The results of the microspectrophotometric measurements support the idea that the basic protein lost from the spermatid nucleus is the source of the basic protein in the sphère chromatophile.

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