The incorporation of radioactive phosphorus into the nucleic acids of different rabbit tissues.

In a previous paper (Smellie, McIndoe, Logan, Davidson & Dawson, 1953) we have discussed the incorporation of radioactive phosphorus (82p) into the deoxyribonucleic acid (DNA) of the cell nucleus of rabbit liver and into the ribonucleic acid of the nucleus (nRNA) and of the various cytoplasmic fractions (cRNA) at different times after administration of the isotope. Asmightbe expected in a non-proliferating tissue, the incorporation into the DNA was only slight. On the other hand, the incorporation into the cRNA was relatively great and at a maximum at about D0 hr. after administration, while that into the nRNA was even greater and at a maximum at about 18 hr. It is known from the early work of Hevesy & Ottesen (1943) and of Andreasen & Ottesen (1945) that incorporation of 32p into DNA is greater in those tissues in which mitotic division is active, e.g. bone marrow and intestinal mucosa, than in resting tissues. But no systematic comparison of incorporation of 32p into DNA, nRNA and cRNA as a function of time has hitherto been made in a series of tissues. Such a study is described in this paper.