THE NATURE OF THE INCREASED RATE OF DNA SYNTHESIS IN SCRAPIE‐AFFECTED MOUSE BRAIN

— In vivo studies have been made of the incorporation of radioactive thymidine into acid insoluble components of control and scrapie‐affected mouse brain. Experiments with hot trichloroacetic acid extracts of brain and with purified preparations of DNA have confirmed that there is an increased rate of DNA synthesis in scrapie brain which is entirely associated with nuclei. No increase was found in the rate of DNA synthesis in cytoplasmic fractions of scrapie brain. Hydroxyapatite chromatography of heat denatured and renatured DNA suggests that in scrapie brain there is a similar increase in the rates of synthesis of the poorly, moderately and highly reiterated (i.e. satellite) species of nuclear DNA. Experiments involving brain dissection indicate that the increased rate of DNA synthesis in scrapie does not take place exclusively in the subependymal layer of the lateral ventricles. From these and previously reported studies using radioautographic techniques it is concluded that the increased DNA synthesis in scrapie brain is not associated specifically with cells undergoing mitosis.