Changes in basic chromosomal proteins during spermatogenesis in the mature rat

Nuclei of the seminiferous epithelial cells of rat testis were filtered through glass wool to remove sperm heads, flagellae and late-stage spermatids and then centrifuged through sucrose gradients to yield three fractions. The cellular origins of the predominant nuclei in these fractions were identified through the kinetics of labeling with [ 3H]thymidine. The relative amounts of the different histone fractions changed during the various stages of spermatogenesis in an interesting and systematic manner. For example, the ratio of the trailing (acetylated) to the leading member of the histone F2a1 doublet was greater in spermatid nuclei than in nuclei of a fraction enriched in primary spermatocytes. Similarly, the ratio X 1 F1 was greatest in spermatid nuclei. On the other hand, the ratio X 3 F2b was greater in the nuclei of pachytene-diplotene primary spermatocytes than in the fraction enriched in nuclei of spermatogonia and preloptotene primary spermatocytes. A basic protein fraction with some of the properties of a protamine was extracted from rat sperm heads and from the nuclei of spermatids. This protein fraction has high contents of arginine and cysteine (after reduction), and it appears to be identical with the protamine described by Kistler et al. In addition, a new protamine was isolated from rat sperm heads which has high arginine content but appears to be devoid of lysine and cyst(e)ine. Two other basic protein fractions with high electrophoretic mobilities were extracted with acid from the nuclei of testicular seminiferous epithetial cells without prior reduction. One of these proteins may be identical with the testis-specific protein of Kistler et al.