Interaction of tyrosyl, histidyl, and tryptophanyl peptides with DNA: specificity and mechanism of the interaction.

In the Tyr-(Gly)(1-4)-Tyr series maximal thermal stabilization of calf thymus DNA (deltaT(m)=10 degrees ) occurred with the Tyr-(Gly)(2)-Tyr peptide, where three base pairs could separate the two tyrosyl residues. Tyr-Gly-Tyr-Gly-Tyr stabilized the DNA by 6 degrees . The alternating Trp-Gly-Trp-Gly-Trp and His-Gly-His-Gly-His peptides were equally as effective as the Tyr-Gly-Tyr-Gly-Tyr peptide in stabilizing calf thymus DNA against thermal denaturation. But the alternating Phe-Gly-Phe-Gly-Phe peptide afforded little stabilization, suggesting that a sidechain possessing both a conjugated pi-electron system and an electron donor atom is necessary for DNA stabilization. Introduction of electron withdrawing iodo or nitro group into the tyrosyl sidechains almost completely abolished the stabilizing effect. Although the tyrosyl peptides seem to be specific for GC-base pairs, no correlation was found in natural DNA between% GC and% thermal stabilization. Eukaryotic DNAs showed twice the stabilization of prokaryotic DNAs with the same GC content.