DNA AGGREGATION INDUCED BY POLYAMINES AND COBALTHEXAMINE

We have studied the precipitation of short DNA molecules by the polyca tions spermidine, spermine, and cobalthexamine. The addition of these cations to a DNA solution leads first to the precipitation of the DNA; further addition resolubilizes the DNA pellet. The multivalent salt c oncentration required for resolubilization is essentially independent of the DNA concentration (between 1 mu g/ml and 1 mg/ml) and of the mo novalent cation concentration present in the DNA solution (up to 100 m M). The DNA aggregates are anisotropic; those obtained in the presence of the polyamines spermidine and spermine generally contain a cholest eric liquid crystalline phase that flows spontaneously. In contrast th is phase is never seen in the presence of cobalthexamine. We propose t hat the ability of polyamines to condense DNA in fluid structures is a n essential feature of their biological functions.