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SEDIMENTATION ANALYSIS OF DNA PHOTOOXIDIZED IN THE PRESENCE OF THIOPYRONINE |
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| Authors: | H. Triebel,H. Bä r,H-E. Jacob,E. Sarfert, H. Berg |
| Affiliation: | *Akademie der Wissenschaften der DDR, Forschungszentrum für Molekularbiologie und Medizin, Zentralinstitut für Mikrobiologie und experimentelle Therapie, Abteilungen Biophysikochemie, DDR-69 Jena, E. Germany;**Akademie der Wissenschaften der DDR, Forschungszentrum für Molekularbiologie und Medizin, und Biochemie, DDR-69 Jena, E. Germany |
| Abstract: | Abstract. Illumination of single-stranded φ×174 phage DNA with visible lightλ > 500 nm) in the presence of the sensitizer thiopyronine results in both chain scissions detectable by velocity sedimentation in neutral medium and in alkali-labile bonds which yield secondary strand breaks after alkaline treatment. Compared with the generation of primary strand breaks, the formation of alkali-labile sites seems to be the predominant reaction. Photodynamic treatment of homogeneous double-stranded Ta, phage DNA leads to changes in the overall conformation of DNA as revealed by an initial increase of the sedimentation coefficient. The simultaneous occurrence of different effects (decrease of molecular weight, increase of effective DNA flexibility) is particularly evident from changes in the sedimentation coefficient distribution. The fact that both processes influence the sedimentation behaviour questions the common procedure of calculating double-strand break numbers from sedimentation coefficient distributions on the basis of s#-M relations which are valid for intact DNA only. Photooxidized double-stranded DNA exhibits an increased sensitivity against shear forces. |
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