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

^a Laboratory of Molecular Biology and Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

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.

¹ Present address: School of Basic Sciences, U.P. Agricultural University, Pantnagar, Nainital, (U.P.), India.

² Present address: Rosenstiel Basic Medical Research Center, Brandeis University, Waltham, Mass. 02154.