Cationic metal-specific structures adopted by the poly(dG) region and the direct repeats in the chicken adult βA globin gene promoter

Abstract

Naturally occurring contiguous deoxyguanine residues and their surrounding sequences in the chicken adult βA globin gene promoter were analyzed for their inherent potential to adopt non-B DNA structures in supercoiled plasmid DNA. In particular, cationic effects on structure were studied by treating the supercoiled plasmid DNA harboring the chicken adult βA globin 5′ flanking sequence with an unpaired DNA base-specific probe, chloroacetaldehyde in the presence of either Mg++ , Cu++ , Zn++ , Ca++ or Co++ ions. The chloroacetaldehyde-reactive bases were mapped at a single base resolution by a chemical cleavage method that specifically cleaves DNA at the chloroacetaldehyde modified sites. These experiments revealed that while Mg++ and Ca++ ions induce a dG-dG-dC triple helix structure at the contiguous dG residues, Zn++ , Cu++ and Co++ ions induce yet another structure at the direct repeats immediately 5' of the dG residues. When Mg++ and Zn++ ions are both present, Zn++ inhibits the dG-dG-dC triplex at the contiguous dG residues and induces a particular non-B DNA structure at the adjacent direct repeats. The specific induction of non-B DNA structures by metal ions at the two adjacent sequences within the promoter region may be of biological significance. © 1989 IRL Press at Oxford University Press.