Thermostability of double-stranded deoxyribonucleic acids: the effects of covalent additions of a psoralen

Abstract

ABSTRACT: We have carried out a thermodynamic study on the effects of covalent additions of the psoralen derivative H M T, 4’-(hydroxymethyl)-4,5’,8-trimethylpsoralen, on the stability of double-stranded deoxy-oligonucleotides. This was done with two systems. The first was a double-stranded D N A formed by two non-self-complementary oligonucleotides, 5’-GAAGCTACGAGC-3 ’ and S-GCTCGTAGCTTC-3’, where we site specifically placed an H M T molecule on the thymidine residue in oligonucleotide 5’-GAAGCT-ACGAGC-3 ’ as either a furan-side monoadduct or a pyrone-side monoadduct. The second was a dou-ble-stranded D N A formed by a self-complementary oligonucleotide, 5’-GGGTACCC-3’, where we placed an H M T molecule on the thymidine residue of each strand as a furan-side monoadduct or cross-linked the two strands with an H M T molecule linked to the two thymidines. We found that H M T cross-linking of the two strands stabilizes the double helix formed by 5’-GGGTACCC-3’, as one might expect. Less predictable results were that the monoaddition of a psoralen stabilizes the double helix formed by the two non-self-complementary oligonucleotides by as much as 1.3 kcal/mol as a furan-side monoadduct and 0.7 kcal/mol as a pyrone-side monoadduct a t 25 O C in 50 m M NaCl. In contrast, the monoaddition of a psorale