Resolution of α, β and γ DNA of Saccharomyces cerevisiae with the antitumor drug cis-Pt(NH 3) 2Cl 2. Evidence for preferential drug binding by GpG sequences of DNA

Abstract

This paper reports further studies on the separation of DNAs with the antitumor drug cis-Pt(NH 3) 2Cl 2. cis-Pt(NH 3) 2Cl 2 permits resolution of the three DNA components from whole Saccharomyces cerevisiae in CsCl gradients, avoids pelleting of mitochondrial (β) DNA and does not require a critical molar ratio of platinum drug to DNA-P. However, the difficulty in removing all of the DNA-bound platinum may limit its preparative use. The linear relationship between the increase in buoyant density of platinized double-stranded DNA and its G + C content is employed to calculate a G + C content of 41.2% and 45.8% for α and γ DNA, respectively, using a value of 20% G + C for β DNA. In parallel experiments, we find that poly(dG)·poly(dC), which contains sequential guanine bases, exhibits an unexpectedly large buoyant density increase with cis-Pt(NH 3) 2 Cl 2, while the buoyant density increase of poly[d(G-C)]is markedly retarded, indicating an effect of nucleotide base sequence on DNA separation. The trans platinum compound, which has no antitumor properties, separates DNAs on the basis of G + C content in a similar fashion, but does not preferentially increase the buoyant density of poly(dG)·poly(dC).