The incorporation of phosphorus into fractions of Escherichia coli made by centrifuging and by chemical means

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Abstract
Growing cells of E. coli were exposed to P32O43 for about one-fifth of their generation time, and disintegrated and fractionated into a heavy particulate fraction (R1), a light particulate fraction (R11) and a soluble fraction (S11). The unfractionated disintegrate and its 3 fractions were then chemically fractionated by the Schmidt and Thannhauser J. Biol. Chem. 161: 83. (1945) method and the specific activities of these fractions determined. Of the acid-insoluble phosphates in the unfractionated disintegrate the highest rate of incorporation is into the phospholipids and the lowest into ribonucleic acid. When account is taken of the presence in the deoxyribonucleic acid fraction of a heavy, more highly active contaminant, however, deoxyribonucleic acid is observed to exhibit the lowest rate of incorporation. Interesting differences exist between the sedimentation fractions. Acid-soluble phosphates with high specific activities are located mainly in S11. The concentration and specific activity of phospholipid decreases as the particle size decreases. The rate of incorporation into ribonucleic acid is highest in Rl and lowest in Rll. Authentic deoxyribonucleic acid with low specific activity is located mainly in S11. Of all the nucleic acid fractions examined, the lowest rate of phosphorus incorporation is into a ribonucleic acid constituent of R11. The results confirm the heterogeneity of ribonucleic acid suggested previously by its staining properties and its sedimentation behavior but do not furnish evidence that "fluctuating ribonucleic acid" is a precursor of deoxyribonucleic acid.