CALICHEAMICIN-MEDIATED DNA-DAMAGE IN A RECONSTITUTED NUCLEOSOME IS NOT AFFECTED BY HISTONE ACETYLATION - THE ROLE OF DRUG STRUCTURE IN THE TARGET RECOGNITION PROCESS

We have examined the role of drug structure and histone acetylation in DNA damage produced by the enediyne antibiotic calicheamicin gamma(1) (I) in nucleosomes reconstituted onto the 5S rRNA gene of Xenopus bore alis. Consistent with previous observations, calicheamicin damage at t he 3'-end of a purine tract (positions -13 and -14) was enhanced in th e nucleosome compared to naked DNA while damage at other sites was som ewhat reduced in the nucleosome. However, damage produced by esperamic in C, an analog of calicheamicin missing the terminal sugar-aromatic r ing in the side chain, showed no enhancement at positions -13 and -14, and its sequence selectivity in naked DNA was markedly different from that of calicheamicin. This highlights the importance of the intact t etrasaccharide side chain in the recognition of the structural deforma tion occurring at the 3'-ends of purine tracts. Both drugs produced id entical cleavage patterns in normal and hyperacetylated nucleosomes. G iven the sensitivity of calicheamicin to local DNA conformation, this observation is consistent with other studies that suggest that histone acetylation alone does not significantly affect the local conformatio n of core DNA in the nucleosome.