THE INTERACTION OF HEDAMYCIN AND DC92-B IN A SEQUENCE SELECTIVE MANNER WITH DNA IN INTACT HUMAN-CELLS

The sequence specificity of the pluramycin antibiotics hedamycin and D C92-B, was established in intact human cells using a linear amplificat ion system. In this system an oligonucleotide primer is extended by Ta g DNA polymerase up to a damage site. The products are run on a DNA se quencing gel and the damage can be determined to the exact base pair. The human repetitive alpha RI DNA was used as the target DNA sequence for these experiments. It was found that G residues were the main site of adduct formation, for both hedamycin and DC92-B. The sequences 5'- TGT and 5'-CGT were the most intense sites of DNA damage. A comparison of the DNA damage intensity in intact cells and purified DNA revealed that the sequence position of adduct formation was very similar in th e two environments. However, a densitometric comparison of the damage intensity in the two environments revealed significant differences. Tw o regions were found (120 and 130 bp in length) where the damage inten sity was relatively lower in intact cells compared to purified DNA. Bu t at the boundaries of these sequences, there were regions (approx. 50 -60 bp long) that were relatively more damaged in intact cells compare d to purified DNA. One explanation of this phenomenon is the presence of a protecting nucleosome core on each of the 120/130 bp regions and flanking nucleosome linker regions of 50-60 bp. This postulated sequen ce phasing of the nucleosomes corresponds almost exactly with the majo r nucleosome phasing found in African green monkey cells. Also the cen tromere protein B binding site is found in the border region between t he nucleosome core and linker DNA regions. Hedamycin and DC92-B produc ed nearly identical results in this human cell system.