Modified alkaline elution allows the measurement of intact apurinic sites in mammalian genomic DNA

The presence of apurinic/apyrimidinic (AP) sites in cell genomes is known t o be toxic and mutagenic. These lesions are therefore repaired in cells by efficient enzymatic systems. However, a report (Nakamura and Swenberg, Canc er Res. 59 (1999) 2522-2526) indicates an unexpected high rate of endogenou s apurinic/apyrimidinic (AP) sites in genomic DNA in mammalian tissues. The technology used does not allow the authors to distinguish between intact A P sites and 3'cleaved AP sites. The corresponding values range between 2 an d 4 sites per million of nucleotides in various human and rat tissues. Usin g a modified alkaline elution method we show here that the stationary level of intact AP sites is about 0.16 per million of nucleotides in leukemic mo use L1210 cells. (C) 2000 Societe francaise de biochimie et biologie molecu laire / Editions scientifiques et medicales Elsevier SAS.