UTILIZATION OF THYMIDINE-C14 BY BONE MARROW CELLS AND ISOLATED THYMUS NUCLEI

Abstract

The main goal of these studies has been to obtain a cell-free system capable of utilizing thymidine-Cl4 for the biosynthesis of deoxyribonucleic acid (DNA).Although minced chick embryo was active in vitro (I), further disruption by homogenization inevitably yielded inactive preparations.A survey of various tissues of the rabbit showed that bone marrow and thymus very actively utilized thymidine-Cl4for DNA synthesis in vitro, a result expected in view of the known high mitotic activity of these tissues.A simplified assay for thymidine uptake into DNA was developed, consisting of measuring the radioactivity of the acid-insoluble fraction.This procedure was possible since earlier work showed that ribonucleic acid was not labeled with thymidine-Cl4 as a precursor (1).Incorporation of thymidine into chicken bone marrow DNA was studied by use of the new assay under a variety of conditions.The addition of lyophilized bone marrow was found to be stimulatory for the uptake of thymidine by washed bone marrow cells.DNA fractions with different specific activities were isolated from bone marrow incubated with thymidine-C4.Progress was made toward the goal of a cell-free system capable of DNA synthesis by the use of isolated rabbit thymus nuclei (2) for uptake studies with thymidine-C14.EXPERIMENTAL