THE INCORPORATION OF TRITIUM FROM THYMIDINE INTO PROTEINS OF THE MOUSE

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Abstract
Tritium from methyl-H3-thymidine was Incorporated into proteins of mice to the level of 1 to 10% of the injected doses. Tritiated water was not an intermediate. Transmethylation reactions are proposed as a means whereby certain amino acids might have acquired the tritium from thymidine during catabolism. The initial (2 hr.) ratios of DNA to protein tritium activities per milligram of wet tissue ranged from 5 in 2 tissues of low DNA synthetic activity (pancreas, liver) to 35 to 40 in 2 tissues of high DNA synthetic activity (spleen, small intestine). Labeled nuclear protein was coincident with labeled DNA in nuclei, where it constituted less than 2.5% of the total tritium.