A rapid assay for DNA repair synthesis using neutral and alkaline sodium iodide gradients

A modification to the method for estimation of repair DNA synthesis in cultured mammalian cells using density labeling which reduces the time and labor involved is described. Centrifugation times are reduced by using high-molecular-weight DNA which is loaded onto the top of a preformed sodium iodide gradient. Cerenkov counting is used to locate the region of the gradient containing light DNA for rebanding and likewise to identify appropriate fractions from alkaline gradients for acid precipitation for scintillation counting. The procedures give results indistinguishable from cesium chloride equilibrium gradients in a shorter time, with less effort, and at a lower cost.