Modulation of enediyne-induced DNA damage by chromatin structures in transcriptionally active genes

To better understand how the cellular environment of DNA affects it as a target for genotoxins, we have used ligation-mediated PCR to map DNA damage produced by two DNA-cleaving enediyne antibiotics, esperamicins Al and C, in the transcriptionally active human p53 and phosphoglycerate kinase (pgk1) genes in vivo. Esperamicin Al, which is limited to damaging the linker region between nucleosome cores due to intercalation of an anthranilate moiety, did not detect the presence of a nucleosome proposed to reside between exons 5 and 6 of p53. This may be due to the absence of a nucleosome at this site in the p53 gene or to the altered structure of nucleosomes in transcriptionally active genes. In studies of the upstream region of the active pgk1 gene, we found that DNA damage produced by both enediynes was enhanced in sequences located between several transcription factor binding sites, while patterns of DNA damage within the binding sites were consistent with known drug binding modes and structures of the protein-DNA complexes. For both drugs, the DNA sequence appeared to be the major determinant of the location of DNA damage, with chromatin structures modulating the quantity of DNA damage.