Oligonucleotide photoproducts formed by photolysis of polyribobromouridylic acid

The cyclobutane dimers of 2'-deoxyuridine, 2'-deoxycytidine, 5-methyl-2'-deoxycytidine and 5-bromo-2'-deoxyuridine

Irradiation of DNA and RNA pyrimidine nucleosides with UV light in frozen aqueous solution or in solution with acetone often results in the formation of cyclobutane dimers (CBDs). Many of these photodimers have not been characterized. We present here the results of work designed to achieve the isolation, spectroscopic characterization and determination of the stereochemical nature of a number of little studied or previously unstudied CBDs of four 2'-deoxyribonuclesides. These nucleosides are 2'-deoxyuridine (dUrd), 2'-deoxycytidine (dCyd), 5-methyl-2'-deoxycytidine (5-MedCyd) and 5-bromo-2'-deoxyuridine (5-BrdUrd). In particular, we have isolated and characterized six dUrd CBDs, five dCyd CBDs, five 5-MedCyd CBDs and four 5-BrdUrd CBDs. Photoproducts were studied by UV spectroscopy, mass spectrometry, proton NMR spectroscopy and via chemical approaches. Also presented are results from less definitive studies of a number of (6-4) (or 5-4) photoadducts of these nucleosides. In addition, results from exploratory photochemical studies of other 2'-deoxyribonucleosides in frozen solution, as well as some mixtures of two nucleosides, are given. The latter results indicate that 5-iodo-2'-deoxyuridine (5-IdUrd), 5-bromo-2'-deoxycytidine and 5-iodo-2'-deoxycytidine each form putative CBDs and that 5-BrdUrd is capable of forming putative mixed CBDs and (6-4) and/or (5-4) adducts with thymidine (Thd); 5-IdUrd similarly forms a (6-4) (or (5-4)) adduct with Thd.

Enzymatic digestion of DNA gamma-irradiated in aqueous solution separation of the digests by ion-exchange chromatography

Aqueous solutions of DNA were gamma-irradiated in the presence and absence of oxygen and enzymatically hydrolysed by the combined action of pancreatic deoxyribonuclease (DNase I), snake-venom phosphodiesterase (PDE I), spleen phosphodiesterase (PDE II) and alkaline phosphatase. In contrast to unirradiated DNA, which is fully hydrolysed to nucleosides by these enzymes, gamma-irradiated DNA yields a series of oligonucleotides. Their isolation might enalbe the future identification of the chemical nature of DNA lesions.

The lesions produced by ultraviolet light in DNA containing 5-bromouracil

The compound 5-bromouracil (BrU) may be incorporated into DNA in place of its analog thymine. This review is concerned with the photochemical lesions produced by the action of ultraviolet light on such BrU-DNA, and consequent biological effects of such lesions.