Interactions of poly(N epsilon, N epsilon, N epsilon-trimethyllysine) and poly(N delta, N delta, N delta-trimethylornithine) with polynucleotides: salt dissociation and thermal denaturation.

The interaction of poly(N epsilon, N epsilon, N epsilon-trimethyl-L-lysine) ([Lys(Me3)]n) and poly(N delta, N delta, N delta-trimethyl-L-ornithine) ([Orn(Me3)]n) with polynucleotides was studied by thermal denaturation, viscosity, and dissociation by salt. The methylated polymers decrease the viscosity of DNA in proportion to the amount of bound peptide. [Lys(Me3)]n and [Orn(Me3)]n raise Tm of polynucleotides more than do (Lys)n and (Orn)n. Dissociation of the polypeptide-polynucleotide complexes with NaCl, KCl, or MgCl2 required about half the salt concentration for the methylated polymers as for the parent polymers. The effects of Tm on DNA appear to be complex and may involve differences in the hydrophobic effects, solvation, and conformational entropy. The salt dissociation data are discussed in relation t the role of histone methylation in chromatin function.