INTERACTION OF BASIC OLIGO-L-AMINO ACIDS WITH DEOXYRIBONUCLEIC ACID - OLIGO-L-ORNITHINES OF VARIOUS CHAIN LENGTHS AND HERRING SPERM DNA

The interaction of native DNA from herring sperm with oligo-l-ornithines having definite chain lengths of between 2 and 18 residues (prepared by chromatographic fractionation of a partial acid hydrolysate of poly-l-ornithine), has been studied in order to increase our knowledge of the fundamental phenomena underlying the interaction between DNA and basic nuclear proteins. DNA-oligo-l-ornithine complexes were prepared by two different procedures: (i) the direct mixing method and (ii) the dialysis method. The results are summarized as follows. 1. 1 Addition of the oligomers always resulted in the stabilization of double-stranded DNA against thermal denaturation, though marked differences in melting profiles were observed, which were dependent either on the chain length of the oligomers or to the method of complex formation. 2. 2 The binding of (Orn)n to DNA is reversible and in a state of equilibrium when n ≦ 6 under the ionic condition employed. Differences in the stabilizing effect of DNA are observed for (Orn)n when n = 2-4, by comparing the values of ΔTm (max.); these values are comparable for (Orn)n when n = 4-6. 3. 3 For (Orn)n, where n = 8-9, two kinds of complexes with different stabilities are formed between DNA and the oligopeptides. 4. 4 For (Orn)n, where n = 18, binding of an irreversible nature predominates when the ionic strength of salt is low. The complex formed by the dialysis method is more stable than the one formed by the mixing method. © 1969.