DISTORTION AFTER MONOFUNCTIONAL ALKYLATION BY MITOMYCIN-C OF A DODECAMER CONTAINING ITS MAJOR BINDING-SITE

The structural distortions of the duplex dodecamer d(ATTAACGTTAAT)(2) monofunctionally alkylated by mitomycin C have been studied by the use of chemical probes reactivity and resonance Raman spectroscopy. This sequence contains the 5'-ACGT sequence for which mitomycin C was deter mined to present the best affinity (S. Kumar, R. Lipman, and M. Tomasz , Biochemistry 31, 1399 (1992)). Raman spectroscopy as well as osmium tetroxyde reactivity indicate that the distortion of the double helix structure is located around the central CG bases. Mitomycin C reacts e xclusively with the 2-amino group of guanine and this binding does not disrupt the inter bases H-bonds, as indicated by chloroacetaldehyde r eactivity. Although resonance Raman spectroscopy does not allow the ha ndedness of the monoalkylated CG/GC sequence to be determined, it indi cates a similarity between the base stacking and that which would be o bserved for alternating purine/pyrimidine sequences at high salt conce ntration.