Interactions of poly (N epsilon , N epsilon , N epsilon ,-trimethyllysine) and poly(lysine) with polynucleotides: circular dichroism and A-T sequence selectivity.

Complexes of (Lys) and [Lys(Me3)]n with natural and synthetic DNAs have been studied by CD as a function of ionic strength. In dilute EDTA, (Lys)n and [Lys(Me3)]n produce the same distortions to the CD spectrum of calf thymus DNA at r (peptide residue/nucleotide residue) values less than 0.6. At higher r values, the distortions are somewhat different. [Lys(me3)]n alters the conformation of some polynucleotides differently from (Lys)n under non- psi conditions. Therefore, methylation of histones may serve to alter the structure of chromatin. At low ionic strength, [Lys(Me3)]n and (Lys)n alter the viscosity of DNA to the same extent between r values of 0.0 and 1.0. In contrast to (Lys)n-DNA, at high ionic strengths, [lys(Me3)]n-DNA does not show psi - type CD spectra. (Lys)n forms psi - structures with (dA-dT)n and (dG-dC)n. [Lys(Me3)]n forms psi + structures with (dA-dT)n. Between 0.05 and 0.3 M NaCl, [Lys(Me3)]n forms psi+ structures with (dG-dC)n, while between 0.35 and 0.45 M NaCl, it forms a psi - structure with (dG-dC)n. Neither (Lys)n nor [Lys(Me3)]n forms psi structures with (dA)n.(dT)n or (dG)n.(dC)n. These results, in conjunction with the work of others on reconstitution of nucleosome-like particles from synthetic polynucleotides, suggest that the ability of DNA and histones to form nucleosomes is related to the formation of psi structures. (Lys)n binds preferentially to (dA)n.(dT)n over (dA-dT)n. [Lys(Me3)]n binds to (dA)n.(dT)n and (dA-dT)n with equal affinity.