Dissociation of the AT-specific bifunctional intercalator [N-MeCys³,N-MeCys⁷]TANDEM from TpA sites in DNA

Fletcher, M. C., Olsen, R. K. and Fox, K. R. (1995) Dissociation of the AT-specific bifunctional intercalator [N-MeCys³,N-MeCys⁷]TANDEM from TpA sites in DNA. Biochemical Journal, 306 (1), 15-19. (doi:10.1042/bj3060015).

Abstract

We have examined the dissociation of [N-MeCys³,NMeCys⁷]TANDEM, an AT-selective bifunctional intercalator, from TpA sites in mixed-sequence DNAs by a modification of the footprinting technique. Dissociation of complexes between the ligand and radiolabelled DNA fragments was initiated by adding a vast excess of unlabelled calf thymus DNA. Portions of this mixture were subjected to DNAse I footprinting at various times after adding the competitor DNA. Dissociation of the ligand from each site was seen by the time-dependent disappearance of the footprinting pattern. Within a natural DNA fragment (tyrT) the ligand dissociates from TTAT faster than from ATAT. We found that the stability of complexes with isolated TpA steps decreases in the order ATAT > TTAA > TATA. Dissociation from each of these sites is much faster than from longer regions of (AT)(n). These results confirm the requirement for A and T base-pairs surrounding the TpA step and suggest that the interaction is strongest with regions of alternating AT, possibly as a result of its unusual structure. The ligand dissociates more slowly from the centre of(AT), tracts than from the edges, suggesting that variations in dissociation rate arise from sequence-dependent variations in local DNA structure.

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Contributors

Author: K. R. Fox

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