Changes in the Metabolism of Ribonucleic Acid Preceding the Synthesis of Deoxyribonucleic Acid in Mammalian Cells Cultured from the Animal

Abstract

Mammalian kidney is generally characterized by a low mitotic rate and a correspondingly low rate of DNA formation.Nevertheless, when rabbit kidney cortex was gently treated with trypsin (to avoid extensive cellular disaggregation) and supplied with a growth medium free of animal serum, it was observed that at least half the cells proceeded to synthesize DNA (1).Synthesis began, however, only after a lag period of more than 30 hours.When it was found that the lag period was a time of intense metabolic activity, three broad questions were raised.(a) What cellular changes occur in vitro which initiate the reactions of the lag period?(h) What kinds of reactions, requisite for the later formation of DNA, occur during the lag period?(c) In what manner do these reactions lead to DNA synthesis?That changes in RNA and protein metabolism occurred during the lag period has been reported (I).These included a greater than 2-fold increase in cellular RNA (acid-precipitable pentose) and an almost 1.5-fold increase in cellular protein.The importance of at least a part of the newly synthesized RNA and protein follows from the observation that inhibition of t,heir formation resulted in suppression of DNA formation.The present report describes some of the changes in RNA metabolism that occur during the first day of incubation of the trypsin-treated kidney cells and attempts to relate these changes to the subsequent synthesis of DNA. EXPERIMENTAL PROCEDUREMaterials-The components of the culture medium and the source of several of the preparations used have been previously described (1).Actinomycin D was kindly provided by Dr. Elmer Alpert, Merck Sharp and Dohme Research Laboratories, and mitomycin C was obtained from Kyowa Fermentation Industry,