Studies on Deoxyribonucleic Acids and Nucleoproteins

II. Tritiation of Deoxyribonucleic Acids

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1. Deoxyribonucleic acids of calf thymus and chick embryo were tritiated by the exposure to gaseous tritium. The tritiation did not affect at all the base composition but their ε(P) values increased in a limited extent (Table I).
2. The labelled DNAs were analyzed on specific radioactivities of base, deoxyribose and deoxyribonucleoside as well as residual protein.
3. Calf thymus DNA was hydrolyzed with deoxyribonuclease and a snake venom (‘Habu’) and components were isolated and purified. Among the bases, thymine was the most radioactive (7×10⁶sc.p.m./μmole) as compared with guanine, adenine and cytosine (Table II).
4) Deoxyribose isolated from deoxy-guanosine and -adenosine had the same radio-activity, 5-6×lO⁴ c.p.m./μmole. At the level of deoxyribonucleoside, the specific radioactivity of thymidine was less than those of others (Table III) and, from the non-dialyzable fraction of the enzyme hydrolyzate, a highly active portion of thymine was found (Table IV).
5) Among amino acids of the residual protein, glycine and alanine contained higher radioactivities than other amino acids in both calf thymus and chick embryonal DNAs.
6) The susceptibility of tritiated DNA against hydrolyzing enzymes and the distribution of radioactivity of thymine were discussed.
The authors wish to thank Dr. A. Ohsaka for the supply of the snake venom (‘Habu’).