Perturbations in cell cycle progression from radioactive DNA precursors

RADIOACTIVE precursors of DNA have widespread application in eukaryotic cell systems for studies of kinetic phenomena, such as DNA metabolism and cell population growth, and for labelling DNA 1,2 for biophysical or biochemical investigations. Implicit in their use is the assumption that the experimental endpoints are not perturbed by the presence of the labelling isotope(s). But the validity of this assumption requires reevaluation in the light of reports that the incorporation of radioactive compounds into cellular DNA causes significant biological anomalies, including mutations, chromosome aberrations, cell death 3 , growth retardation and strand breaks in the DNA molecule 4 (for reviews see refs 5 and 6). At least one investigator 5 has advocated separate evaluation of the potential perturbations in every experimental system using radioisotope-labelled nucleic acid precursors.