Bloch and Gabriel

Desoxyribonucleic acid (DNA) appears to play a primary role in the maintenance of genetic continuity of cells throughout reproduction, cell growth, and differentiation. I t has been demonstrated to transmit hereditary characters in microorganisms (Avery a 02. (3), Zamenhott a 02. (38)), and in the higher organisms has been shown to exhibit a constancy in composition (Chargaff (8)), and amount per cell (Boivin a 02. (6), Mirsky and Ris (22), Swift (31, 32)) which might be expected of a genetic determinant. Another of its properties is a remarkable stability, as shown by a low uptake of labelled atoms (Brues a 02. (7), Hammarsten and Hevesy (16)). This uptake has been directly demonstrated by Howard and Pelc (18) and Taylor and McMasters (33) to occur during synthesis of new molecules of DNA. Less is known of nuclear historic, the basic protein associated with DNA. The Vendrelys (34) and Daly d al. (11) have presented evidence suggesting some degree of constancy in composition, and the works of Mirsky and Ris (22), and Alfert and Geschwind (1) indicate a possible constancy in amount per cell in cells of the same tissues. On the other hand, the Stedmans have shown that histone composition does vary from tissue to tissue of the same animal, and from various fractions of the same tissue (29). This variability probably reaches an extreme in the male germ cells of the various species of fish (Kossel (21)), fowl (Daly e~ 02. (12)), plants (D'Alcontres (10)), and invertebrates (Hultin and Herne (19)) in which histone has been found to be replaced by protamine. Daly et 02. (11), Allfrey and Mirsky (2), and Hoberman and Peralta (17) have shown that glycine incorporation into histone is lower than that into the cytoplasmic proteins, yet higher than that into I)NA. I t would appear that, with regard to constancy of amount per cell and stability of composition, the histones are intermediate between the relatively stable I)NA and the metabolic proteins of the cell. The work of Swift (32), Walker and Yates (35), and Patan and Swift (24), has demonstrated that DNA is doubled during interphase before cell division. Further-