Radioactive decays from each of three intracellularly incorporated tritium$\text{compounds}-\text{thymine-methyl-}{}^{3}{\rm H}$ (a DNA precursor),$\text{uracil-}5{}^{3}{\rm H}$ (a RNA precursor), and$\text{histidine-}{}^{3}{\rm H}$ (a protein precursor)-caused degradation of DNA in Escherichia coli as measured by loss of$\text{thymine-}{}^{14}{\rm C}$ label previously incorporated into DNA. Degradation is specific for DNA, as cells labeled with$\text{uracil-}5{}^{3}{\rm H}$ or$\text{histidine-}{}^{3}{\rm H}$ show little loss of these RNA and protein specific precursors, even after extensive loss of$\text{thymine-}{}^{14}{\rm C}$ label. As much as 80% of the cellular DNA was degraded as a result of decays from each of the tritiated compounds; but the rates of degradation varied, being greater for$\text{thymine-methyl-}{}^{3}{\rm H}$ than for$\text{uracil-}5{}^{3}{\rm H}$ and$\text{histidine-}{}^{3}{\rm H}$ decays. The kinetics of DNA degradation for each of these incorporated compounds bear a relationship to each other that is similar to that previously reported for kinetics of inactivation produced by the same compounds in the same cell line.

This content is only available as a PDF.