Accession Number : AD1011020

Title :   UV Laser-Induced DNA Photochemistry

Descriptive Note : Technical Report

Corporate Author : Uniformed Services University Of The Health Sciences Bethesda United States

Personal Author(s) : Masnyk,Taras

Full Text :

Report Date : 13 May 1991

Pagination or Media Count : 139

Abstract : Previous studies examining the effects of UV laser irradiation of nucleosides and nucleotides have determined that qualitative and quantitative differences exist between irradiation at low and high intensities. Multi-photon events involving the singlet and triplet excited states of DNA bases occur following irradiation at high intensity, leading to degradation of bases due to intra-molecular bond cleavage; such events are not seen following irradiation at low intensity. My aim in this work was to extend these studies to conditions of interest to biologists. I irradiated salmon sperm and plasmid DNA in aqueous solution at low (3.15 X 10[expn 7]W/m[expn 2]) , intermediate (2.5 X 10[expn 9] and 1.16 X 10[expn 10] W/m[expn 2]), and high (1.25 X 10[expn 11] W/m[expn 2]) intensities, using a KrF excimer laser emitting at 248 nm. Following irradiation, DNA damage was assayed, with the following findings: 1) pyrimidine cyclobutane dimer and bipyrimidine T(6-4)C photoadduct formation was reduced following irradiation at high intensity relative to low intensity; 2) free thymine and thymine fragments were releasedfrom DNA following irradiation at high intensity, but not at low intensity; 3) DNA strand break formation increased with increasing intensity; 4) double-stranded breaks occurred in DNA following irradiation at high intensity. A mathematical model describing the effect of high intensity UV radiation on plasmid DNA conformation was developed and fit to experimental data on strand breaks. Using the model, dose constants for single- and double-stranded breaks were determined and found to increase with intensity. These results are consistent with the absorption of a second photon by long-lived triplet excited states of DNA following irradiation at high intensity, but not low intensity.

Descriptors :   Photochemistry , deoxyribonucleic acids , Ultraviolet lasers , Excimers , Nucleotides , Nucleosides , Irradiation , Excitation

Distribution Statement : APPROVED FOR PUBLIC RELEASE