Method for Restricting Incorporation of Radioactivity from 3H-Thymidine into Deoxyribonucleic Acid Only During Outgrowth of Spores of Bacillus cereus T

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When heat-activated spores of Bacillus cereus T (thy−) were germinated and grown in medium containing 3H-thymidine, a significant amount of radioactivity was incorporated into ribonucleic acid and deoxyribonucleic acid (DNA). A method was developed to restrict the incorporation of radioactivity from 3H-thymidine into DNA only. This was accomplished by labeling the cells with 3H-thymidine in the presence of 2 mg of 2-deoxyadenosine per ml, 250 μg each of uracil, cytosine, and guanosine per ml, and 500 μg of adenosine per ml. Under these conditions, 97% of the radioactivity incorporated into cold trichloroacetic acid-insoluble material was associated with DNA only. In the absence of these compounds, DNA contained only 72% of the total radioactivity incorporated into cold acid-insoluble material.

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