Strand breaks and alkali-labile bonds induced by ultraviolet light in DNA with 5-bromouracil in vivo

• Published in: Biophysical journal Vol. 24; no. 3; pp. 657 - 664
• Main Authors: Krasin, F., Hutchinson, F.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.1978
• Subjects: Alkalies - pharmacology; Bromouracil - metabolism; Bromouracil - pharmacology; Centrifugation, Density Gradient; Coliphages - drug effects; Coliphages - radiation effects; DNA, Single-Stranded - radiation effects; DNA, Superhelical - radiation effects; DNA, Viral - radiation effects; Escherichia coli - metabolism; Escherichia coli - radiation effects; Nucleic Acid Denaturation; Ultraviolet Rays
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(78)85411-3

Supercircular gamma phage DNA with 10 bromouracils/100 thymine bases, irradiated with 313 nm light in Tris buffer and sedimented on alkaline and neutral gradients, showed 4.6 alkali-labile bonds per true single-strand break, in agreement with Hewitt and Marburger (1975 Photochem. Photobiol. 21:413). The same DNA irradiated in Escherichia coli host cells showed about the same number of breaks in alkaline gradients for equal fluence, but only 0.5 alkali-labile bond per true break. Similarly, E. coli DNA with bromouracil irradiated in the cells showed only 10--20% more breaks when denatured with 0.1 M NaOH than under neutral conditions with 9 M sodium perchlorate at 50 degrees C. These results show that true single-strand breaks occur more frequently than alkali-labile bonds after ultraviolet irradiation of DNA containing bromouracil in cells.