Effects of 2-Thiouracil on Nucleic Acid Metabolism in Roots of Pisum sativum

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Abstract
Segments excised from the roots of pea seedlings and cultured on sintered glass disks with 2% sucrose were incubated with 2-C14 2-thiouracil, harvested after 1, 5, or 25 hr incubation, and incorporation of label into RNA1 (cold HClO4 extractable), RNA2 (non-cold HClO4 extractable), DNA, and the remaining residue was determined. During the first hour the most rapid uptake of label was into the RNA2 fraction with less into RNA1 and none into the DNA or residue. Upon separation of the RNA bases by paper chromatography (acidified methanol as solvent), the activity was found with the uridylic acid. The rate of incorporation of label increased with time. Within 5 hr activity was found in the DNA fractions, and by 25 hr heavy labeling was found in all the fractions, especially the residue. Extraction with 3 N KOH at 70⚬C removed less than half the activity from the residue. The specific activity of the RNA of the following subcellular fractions was determined: nuclei, heavy and light microsomes, fraction X (vesicular material and small mitochondria), and cellular "debris" (mostly cell-wall fragments and nuclei). The most rapid incorporation of label was into the nuclear and X fractions and into the cell debris. The data indicated that 2-thiouracil is incorporated into RNA. It also appears that 2-thiouracil can be metabolized to other compounds which are incorporated into DNA and the cell wall.