title: Binding of Mg2+ to single-stranded polynucleotides: hydration and optical studies.
abstract: The binding of Mg(2+) to single-stranded ribo- and deoxy-polynucleotides, poly(rA), poly(rU), poly(dA) and poly(dT), has been investigated in dilute aqueous solutions at pH 7.5 and 20 degrees C. A combination of ultrasound velocimetry, density, UV and CD spectroscopy have been employed to study hydration and spectral effects of Mg(2+) binding to the polynucleotides. Volume and compressibility effects of Mg(2+) binding to random-coiled poly(rU) and poly(dT) correspond to two coordination bonds probably between the adjacent phosphate groups. The same parameters for poly(rA)+Mg(2+) correspond to an inner-sphere complex with three-four direct contacts. However, almost no hydration effects are arising in binding to its deoxy analog, poly(dA), indicating mostly a delocalized binding mode. In agreement with hydration studies, optical investigations revealed almost no influence of Mg(2+) on poly(dA) properties, while it stabilizes and aggregates poly(rA) single-helix. The evidence presented here indicates that Mg(2+) are able to bind specifically to single-stranded polynucleotides, and recognize their composition and backbone conformation.
authors.affiliation: Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, 1479 Gortner Avenue, St. Paul, Minnesota, MN 55108, USA. bkankia@umn.edu
authors.forename: Besik I
authors.initials: BI
authors.lastname: Kankia
mesh_terms: D000465:Algorithms; D001665:Binding Sites; D002498:Centrifugation; D011232:Chemical Precipitation; D002942:Circular Dichroism; D004277:DNA, Single-Stranded / Q000737:chemistry*; D003720:Densitometry; D008274:Magnesium / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D011061:Poly A / Q000737:chemistry; D011071:Poly T / Q000737:chemistry; D011072:Poly U / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014465:Ultrasonics; D014867:Water / Q000737:chemistry
chemical_list: D004277:DNA, Single-Stranded; D014867:Water; D011061:Poly A; D011071:Poly T; C015465:poly(dA); D011072:Poly U; D008274:Magnesium