Wavelength dependence for the photoreactions of DNA-psoralen monoadducts. 1. Photoreversal of monoadducts

Abstract

We have studied the wavelength dependence for the photoreversal of a monoadducted psoralen derivative, HMT [4''-(hydroxymethyl)4,5'',8-trimethylpsoralen], in a single-stranded deoxyoligonucleotide (5''-GAAGCTACGAGC-3''). The psoralen was covalently attached to the thymidine residue in the oligonucleotide as either as a furan-side monoadduct, which is formed through the cyloaddition between the 4'',5'' double bond of psoralen and the 5,6 double bond of the thymidine, or a pyrone-side monoadduct, which is formed through the cycloaddition between the 3,4 double bond of the psoralen and the 5,6 double bond of the thymidine. As a comparison, we have also investigated the wavelength-dependent photoreversal of the isolated thymidine-HMT monoadducts. All photoreversal action spectral correlate with the extinction spectra of the isolated monoadducts. In the case of the pyrone-side monoadduct, two absorption bands contribute to the photoreversal with a quantum yield of 2 .times. 10-2 at wavelengths below 250 nm and 7 .times. 10-3 at wavelengths from 287 to 314 nm. The incorporation of the monoadduct into the DNA oligomer had little effect upon the photoreversal rate. For the furan-side monoadduct at least three absorption bands contribute to the photoreversal. The quantum yield varied from 5 .times. 10-2 at wavelengths below 250 nm to 7 .times. 10-4 at wavelengths between 295 and 365 nm. In contrast to the case of the pyrone-side monoadduct, the incorporation of the furan-side monoadduct into the DNA oligomer reduced the photoreversal rate constant at wavelengths above 285 nm.