Uptake and subcellular localization of tritiated spermine in Escherichia coli

Abstract

The uptake of tritiated spermine by intact cells of Escherichia coli, as well as spheroplasts, was energy- and temperature-dependent and resulted in the binding of a portion of the spermine to subcellular components in a form not readily exchangeable with unlabeled spermine under the conditions of the experiment. Essentially all the radioactivity found on the cell walls was readily exchangeable. Results from experiments in which spheroplasts were lysed with digitonin and in which phenol-isolated nucleic acid preparations from the lysates were treated with various hydrolytic enzymes can best be explained by postulating that a small but significant part of the spermine was bound to the DNA while a major portion was bound to RNA. Appropriate controls have shown that reequilibration during isolation did not account for the apparent binding to DNA although spermine is bound to the nucleic acids as a salt and is displaced especially from RNA even by moderate concentrations of monovalent cations. The implications of the proposed attachment of spermine to DNA in vivo with respect to the mechanism of the antimutagenic action of spermine are discussed.