Polynucleotides adsorb on mitochondrial and model lipid membranes in the presence of bivalent cations

Abstract

Transfer of polynucleotides across the membrane was demonstrated for prokaryotic [l] as well as for eukaryotic cells [2] . This process involves adsorption of polynucleotides on the cell surface, penetration and release into the cell. The mechanism of crossing the hydrophobic barrier formed by protein-lipid membrane by large hydrophilic molecule is unknown. In particular, the nature of bonds which provide adsorption of polynucleotides on the membranes is unknown. Investigation of this problem with cells is difficult due to the presence of more or less expressed cell wall. Mitochondria can be used as convenient model objects to this end because their outside surface is a ‘pure’ protein-lipid membrane. There exist some experimental data suggesting that RNA can penetrate the mitochondrial membrane. Polynucleotides added to mitochondria stimulate protein synthesis by mitochondrial ribosomes insensitive to exogenous ribonuclease [3-61. Mitochondria contain tRNAs which are coded by the nuclear genome and therefore have to be transferred into mitochondria from the cytoplasm [7] . We demonstrate here that polynucleotides are adsorbed by mitochondrial membranes as well as by liposomes formed either from total mitochondrial lipids or from phosphatidylcholine. The dependence of this adsorption on the presence of Mg2+ permits us to suggest that this interaction is due to action of bivalent cations as crosslinks between phosphate residues of polynucleotides and phosphate residues of the membranes.