title: Strand breaks and alkali-labile bonds induced by ultraviolet light in DNA with 5-bromouracil in vivo.
abstract: 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.
mesh_terms: D000468:Alkalies / Q000494:pharmacology; D001976:Bromouracil / Q000378:metabolism / Q000494:pharmacology*; D002499:Centrifugation, Density Gradient; D003090:Coliphages / Q000187:drug effects / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000528:radiation effects; D004278:DNA, Superhelical / Q000528:radiation effects; D004279:DNA, Viral / Q000528:radiation effects*; D004926:Escherichia coli / Q000378:metabolism / Q000528:radiation effects; D009691:Nucleic Acid Denaturation; D014466:Ultraviolet Rays
chemical_list: D000468:Alkalies; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004279:DNA, Viral; D001976:Bromouracil