DNA-BINDING STUDIES OF MAGNESIUM(II), CALCIUM(II), BARIUM(II) AND ATPCOMPLEXES

We have investigated the ways by which magnesium(II), calcium(II) and barium(II) and their ATP complexes bind to B-DNA. Effects on native ca lf thymus DNA conformation were studied and compared with those involv ing the uncomplexed metal ions and the polymer. It was found that MgAT P(-2), CaATP(-2) and BaATP(-2), interact with the phosphates of the po lynucleotide; only BaATP(-2) appears to bind also through the bases. A TP complexes cause transitions mainly to the B family. The C form is i nduced by small amounts of MgATP(-2) or CaATP(-2). At high complex con centrations (r = 2.5 or 5) the polynucleotide adopts the psi(-) confor mation, while BaATP(-2) induces this transition at r = 0.6. A contribu tion of the A form is observed in the case of CaATP-DNA at r = 0.6 and at the beginning of the reaction in the Ba-DNA system at 22 degrees C , for r = 5. The alkaline earth metal ions induce a stabilization of t he B conformation. Structural changes with magnesium(II) at r = 2.5 ar e interpreted in terms of a B to C transition. Calcium(II) at r = 5 pr oduces the A form. In other cases the alkaline earth metal ions stabil ize the B conformation. It was found that they all interact with the p hosphates of the polynucleotide. The binding ratio, r, is an important factor in an structural changes.