Counterion-induced condensation of deoxyribonucleic acid. A light-scattering study

Abstract

The addition of the trivalent or tetravalent cations spermidine or spermine to a solution of T7 DNA in aqueous solution causes an alteration of the DNA from its extended coil form to a condensed form. If performed at low DNA concentration and at low ionic strengths, this transformation results in a monomolecular collapse to form a particle with a hydrodynamic radius of about 500 A. We have monitored this change using quasielastic and total intensity light scattering. In a solution of 50% methanol in water, the divalent cations Mg2+ and putrescine also can cause the condensation of DNA. Using Manning's (1978) counterion condensation theory, we calculate a striking unity among these disparate ions: the collapse occurs in each case when from 89 to 90% of the DNA phosphate charges are neutralized by condensed counterions.

A novel N-acyl phosphatidylethanolamine-containing delivery vehicle for spermine-condensed plasmid DNA

“…In low salt, the dissociation constant for spermine from DNA is know to be in the m range. 22,54 Therefore, the free concentration of spermine was taken as negligible at the mm spermine concentrations necessary for DNA aggregation in these experiments. The fractional neutralization of the DNA phosphate groups by spermine required for DNA aggregation, ␥, was taken as 0.9 based on the data obtained in the absence of liposomes.…”

“…This is the same value reported to be required for DNA condensation, agreeing with the previous observation that aggregation accompanies condensation at high DNA concentrations. 22,54 Assuming [DNA − spm] = ␥[DNA] total at the point of aggregation and [lipid − spm] = the shift in the curve, one can use the equation…”

“…Polycations of charge +3 or higher, such as polylysine, 17 polyamines [18][19][20] and hexammine cobalt (III), 20,21 have been reported, in vitro, to condense plasmid DNA into much smaller toroid or rod-shaped structures through charge neutralization. 22 Polyamines, such as spermine, can dissociate from DNA at cytoplasmic salt concentrations, potentially releasing the DNA for transport into the nucleus. 18,19,22 Unlike other polycations or cationic lipids, the polyamines, spermidine(3+) and spermine(4+), occur naturally in all living cells.…”

“…22 Polyamines, such as spermine, can dissociate from DNA at cytoplasmic salt concentrations, potentially releasing the DNA for transport into the nucleus. 18,19,22 Unlike other polycations or cationic lipids, the polyamines, spermidine(3+) and spermine(4+), occur naturally in all living cells. 23,24 Millimolar concentrations of polyamines have been found in viruses and bacteria and are involved in packaging of viral and bacterial DNA.…”

Influence of polyamines on membrane functions

“…Moreover, it is now appreciated that protein kinases C represent a family of functional homologous enzymes (Hanks et al, 1988;Nishizuka, 1988). Binding of polyamines to phospholipids At first sight the interaction between polyamines and acidic phospholipids could be considered to be essentially electrostatic and follow the counter-ion condensation theory (Wilson & Bloomfield, 1979), i.e. the affinity increases with the number of positive charges (spermine > spermidine > putrescine) and the net negative charge of phospholipids.…”