DNA condensation in two dimensions.
We have found that divalent electrolyte counterions common in biological cells (Ca(2+), Mg(2+), and Mn(2+) ) can condense anionic DNA molecules confined to two-dimensional cationic surfaces. DNA-condensing agents in vivo include cationic histones and polyamines spermidine and spermine with sufficiently high valence (Z) 3 or larger. In vitro studies show that electrostatic forces between DNA chains in bulk aqueous solution containing divalent counterions remain purely repulsive, and DNA condensation requires counterion valence Z >/= 3. In striking contrast to bulk behavior, synchrotron x-ray diffraction and optical absorption experiments show that above a critical divalent counterion concentration the electrostatic forces between DNA chains adsorbed on surfaces of cationic membranes reverse from repulsive to attractive and lead to a chain collapse transition into a condensed phase of DNA tethered by divalent counterions. This demonstrates the importance of spatial dimensionality to intermolecular interactions where nonspecific counterion-induced electrostatic attractions between the like-charged polyelectrolytes overwhelm the electrostatic repulsions on a surface for Z = 2. This new phase, with a one-dimensional counterion liquid trapped between DNA chains at a density of 0.63 counterions per DNA bp, represents the most compact state of DNA on a surface in vitro and suggests applications in high-density storage of genetic information and organo-metallic materials processing.
Koltover
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Materials Department, Physics Department, and Biochemistry and Molecular Biology Program, University of California, Santa Barbara, CA 93106, USA.
Wagner
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Safinya
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D010582:Bacteriophage lambda / Q000235:genetics; D002413:Cations, Divalent; D002712:Chlorides / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D004279:DNA, Viral / Q000737:chemistry; D005229:Fatty Acids, Monounsaturated / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D015636:Magnesium Chloride / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010713:Phosphatidylcholines / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013095:Spermidine / Q000737:chemistry; D013096:Spermine / Q000737:chemistry
D002413:Cations, Divalent; D002712:Chlorides; D004279:DNA, Viral; D005229:Fatty Acids, Monounsaturated; D008051:Lipid Bilayers; D017895:Manganese Compounds; D010713:Phosphatidylcholines; D000644:Quaternary Ammonium Compounds; D015636:Magnesium Chloride; D013096:Spermine; D003035:Cobalt; D004247:DNA; C017251:1,2-oleoylphosphatidylcholine; C018021:cobaltous chloride; C070046:1,2-dioleoyloxy-3-(trimethylammonium)propane; C025340:manganese chloride; D013095:Spermidine