Lack of Z-DNA Conformation in Mitomycin-Modified Polynucleotides Having Inverted Circular Dichroism
Poly(dG-dC)· poly(dG-dC) and Micrococcus lysodeikticus DNA were modified by exposure to reductively activated mitomycin C, an antitumor antibiotic. The resulting covalent drug-polynucleotide complexes displayed varying degrees of CD inversions, which are strikingly similar to the inverted spectrum observed with Z-DNA. The following criteria have been used to establish, however, that the inverted CD pattern seen in mitomycin C-polynucleotide complexes does not reflect a Z-DNA conformation. (i) The ethanol-induced transition of poly(dG-dC)· poly(dG-dC) from B to Z conformation is not facilitated but rather is inhibited by mitomycin C modification. This may be due to the presence of crosslinks. (ii) Radioimmunoassay indicated no competition for Z-DNA-specific antibody by any of the mitomycin C-modified polynucleotides. (iii) 31P NMR of the complexes yielded a single relatively narrow resonance, which is inconsistent with the dinucleotide repeat characteristic of Z-DNA. Alternative explanations for the inverted CD pattern include a drug-induced left-handed but non-Z conformational change or the superposition of an induced CD onto the CD of B-DNA due to drug-base electronic interactions. These results illustrate the need for caution in interpreting CD changes alone as an indication of Z-DNA conformation.
© 1983 National Academy of Sciences Communicated by Gilbert Stork, January 17, 1983. We thank W. T. Bradner (Bristol Laboratories, Syracuse, NY) for a gift of mitomycin C; R. P. C. Valle for technical assistance with the immunological experiments; and David J. Kaplan (University of Kentucky, Lexington, KY) for his excellent suggestions. This work was supported by PSC-City University of New York Faculty Research Awards (to M.T. and J.K.B.) and grants from the National Institutes of Health (CA 28681 to MT.; GM 32203 to J.K.B.), the Petroleum Research Fund administered by the American Chemical Society (to J.K.B.), and the National Science Foundation (PCM 82-01863 to B.D.S.). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Published - TOMpnas83.pnas.pdf