Nucleic Acids Research, 1985, Vol. 13, No. 15 5645-5656
© 1985
Articles |
Diepoxybutane forms a monoadduct with B-form (dG-dC)n.(dG-dC)n and a crosslinked diadduct with the left-handed Z-form
Department of Biochemistry, Schools of Medicine and Dentistry, University of Alabama at Birmingham, University Station Birmingham, AL 35294, USA
Received June 24, 1985. Accepted July 11, 1985.
The characteristics of the reactions of DL-diepoxybutane (DEB) with (dG–dC)n.(dG–dC)n in the right-handed B-form or the left-handed Z-form were investigated. DEB does react with right-handed B-DNA since less salt is required to convert the modified B-form to Z-form than for the unmodified DNA. However, the product appears to be a monoadduct rather than the crosslinked diadduct formed with the Z-form. The modified B-form can be isolated, converted to a Z-form with lmM MnCl2, and then this activated complex further reacts intramolecularly to give the crosslinked Z-product. This modified Z-form cannot be reverted to the B-form unless the crosslink is cleaved with periodate. Only MnCl2, and to a lesser extent ZnCl2, was effective in facilitating the intramolecular conversion of the B-DNA monoadduct to the Z-DNA diadduct; lmM MgCl2 and 4M NaCl were ineffective suggesting that somewhat different types of modified left-handed conformations were generated by the different salts. DEB also cleaves DNA under our reaction conditions thus precluding studies with supercoiled recombinant plasmids harboring segments that adopt Z-structures.