Digestion of repair sites in rat liver DNA by endogenous nucleases.

The proportion of sheared rat liver DNA recovered from benzoylated DEAE-cellulose in the final stage following stepwise elution with NaCl and caffeine solutions was dependent upon the DNA isolation procedure. An increase in the proportion of DNA containing single stranded regions, consequent upon delay or addition of Mg2+ prior to phenol extraction, suggested nuclease mediated degradation. Administration of methyl methanesulphonate to rats resulted in a consistent proportional increase in the caffeine-eluted fraction. The results of caffeine gradient elution of control and alkylated DNA from benzoylated DEAE-cellulose were consistent with repair-associated single stranded regions being substrates for endogenous single strand-specific exonucleases.