Base and base sequence specificity of the binding of 4-hydroxyaminoquinoline 1-oxide to DNA.

Abstract

Synthetic and natural DNAs we;e reacted with 4-hydroxyaminoquinoline 1-oxide (4-HAQO) in an in vitro enzyme system. The amount of 4-HAQO bound to DNA varied significantly depending on the DNA used. The base sequence as well as the base composition affected the binding. Optical melting profiles of 4-HAQO-modified DNAs were examined. Decrease in the melting temperature and broadening of the transition width were commonly observed. Melting fine structure of lambda-phage DNA became less clear according to the modification. The shape of the melting curves of synthetic polynucleotides was little affected by binding, which suggests that the binding sites are distributed randomly along a DNA molecule. Binding of 4-HAQO to a purine base may distort the secondary structure of neighboring base pairs in a DNA molecule. Degree of the distortion can be estimated as a free energy increment associated with the binding. It was found that the free energy increment differs considerably among the polynucleotides with different base sequences.