Differences in unwinding of supercoiled DNA induced by the two enantiomers of anti-benzo[a]pyrene diol epoxide

Rong Xu, Sheryl Birke, Susan E. Carberry, Nicholas Geacintov, Charles E. Swenberg, Ronald G. Harvey

Research output: Contribution to journalArticle

Abstract

The unwinding of supercoiled φX174 RFI DNA induced by the tumorigenic (+) and non-tumorigenic (-) enantiomers of trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) has been investigated by agarose slab-gel and ethidium titration tube gel electrophoresis. The differences in adduct conformations were verified by flow linear dichroism techniques. Both enantiomers cause a reversible unwinding by the formation of noncovalent intercalative complexes. The effects of covalently bound BPDE residues on the electrophoretic mobilities of the RF I DNA form in agarose gels were investigated in detail in the range of binding ratios rb = 0.0 - 0.06 (covalently bound BPDE residues/nucleotide). In this range of rb values, there is a striking difference in the mobilities of (+)-BPDE- and (-)-BPDE-adducted φX174 DNA in agarose slab-gels, the covalently bound (+)-BPDE residues causing a significantly greater retardation than (-)-BPDE residues. Increasing the level of covalent adducts beyond rb = 0.06 in the case of the (+)-BPDE enantiomer, leads to further unwinding and a minimum in the mobilities (corresponding to comigration of the nicked form and the covalently closed relaxed modified form) at rb 0.10 ± 0.01; at still higher rb values, rewinding of the modified DNA in the opposite sense is observed. From the minimum in the mobility, a mean unwinding angle (per BPDE residue) of θ = 12 ± 1.5° is determined, which is in good agreement the value of θ = 11 ± 1.8° obtained by the tube gel titration method. Using this latter method, values of θ = 6.8 ± 1.7° for (-)-BPDE-φX174 adducts are observed. It is concluded that agarose slab gel techniques are not suitable for determining unwinding angles for (-)-BPDE-modified φX174 DNA because the alterations in the tertiary structures for rb < 0.06 are too small to cause sufficiently large changes in the electrophoretic mobilities. The major trans (+)-BPDE-N2-guanosine covalent adduct is situated at external binding sites and the mechanisms of unwinding are therefore different from those relevant to noncovalent intercalative BPDE-DNA complexes or to classical intercalating drug molecules; a flexible hinge joint and a widening of the minor groove at the site of the lesion may account for the observed unwinding effects. The more heterogeneous (-)-BPDE-nucleoside adducts (involving cis and trans N2-guanosine, and adenosine adducts) are less effective in causing unwinding of supercoiled DNA for reasons which remain to be elucidated.

Original languageEnglish (US)
Pages (from-to)6167-6176
Number of pages10
JournalNucleic Acids Research
Volume20
Issue number23
StatePublished - 1992

Fingerprint

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide
Superhelical DNA
Enantiomers
Benzo(a)pyrene
Epoxy Compounds
Pyrene
DNA
Gels
Sepharose
Electrophoretic mobility
Tube
Titration
Angle
Adenosine
Epoxy
Guanosine
Electrophoresis
Conformation
Range of data
Minor

ASJC Scopus subject areas

  • Genetics
  • Statistics, Probability and Uncertainty
  • Applied Mathematics
  • Health, Toxicology and Mutagenesis
  • Toxicology
  • Genetics(clinical)

Cite this

Xu, R., Birke, S., Carberry, S. E., Geacintov, N., Swenberg, C. E., & Harvey, R. G. (1992). Differences in unwinding of supercoiled DNA induced by the two enantiomers of anti-benzo[a]pyrene diol epoxide. Nucleic Acids Research, 20(23), 6167-6176.

Differences in unwinding of supercoiled DNA induced by the two enantiomers of anti-benzo[a]pyrene diol epoxide. / Xu, Rong; Birke, Sheryl; Carberry, Susan E.; Geacintov, Nicholas; Swenberg, Charles E.; Harvey, Ronald G.

In: Nucleic Acids Research, Vol. 20, No. 23, 1992, p. 6167-6176.

Research output: Contribution to journalArticle

Xu, R, Birke, S, Carberry, SE, Geacintov, N, Swenberg, CE & Harvey, RG 1992, 'Differences in unwinding of supercoiled DNA induced by the two enantiomers of anti-benzo[a]pyrene diol epoxide', Nucleic Acids Research, vol. 20, no. 23, pp. 6167-6176.
Xu, Rong ; Birke, Sheryl ; Carberry, Susan E. ; Geacintov, Nicholas ; Swenberg, Charles E. ; Harvey, Ronald G. / Differences in unwinding of supercoiled DNA induced by the two enantiomers of anti-benzo[a]pyrene diol epoxide. In: Nucleic Acids Research. 1992 ; Vol. 20, No. 23. pp. 6167-6176.
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