Study of X-irradiated DNA using formamide gradients

Abstract

A density gradient of 70–100 % (v/v) formamide was prepared for the study of both native and denatured bacterial DNA. Random single-and double-stranded breaks were introduced by treating the DNA with various doses of X-irradiation. A comparison was then made between two techniques of denaturation : by heating to 100° C followed by immediate cooling, and by gentle heating in high concentrations of formamide. No significant difference was found between the molecular weights of DNA molecules thus denatured. However, the development of this gradient provides a useful tool for centrifugation studies of denatured forms of DNA in a neutral, rather than alkaline environment.