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THE PHOTOCHEMISTRY OF THYMINE AND BROMOURACIL IN VIVO
Author(s) -
Smith Kendric C.
Publication year - 1964
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1964.tb07845.x
Subject(s) - uracil , thymine , cytosine , pyrimidine dimer , chemistry , deamination , photochemistry , dimer , dna , biochemistry , organic chemistry , dna damage , enzyme
. A study of the relative sensitivity of bromouracil and thymine to photochemical alteration (2537Å) when incorporated into the DNA of bacterial cells has led to the conclusion that bromouracil is about twice as reactive as thymine. This offers a chemical basis for the sensitization of bacteria to ultraviolet light by incorporated bromouracil. Bromouracil forms at least five photoproducts in vivo . The relative proportions of these several photoproducts is significantly different in E. coli B/r and Enterococcus Stei. Uracil is the chief photoproduct of bromouracil in Enterococcus Stei but in E. coli B/r the major photo‐product (which is a minor product in Enrerococcus Stei) is as yet unidentified. Preliminary data on the five to nine decomposition products of the dimer of bromouracil and the mixed dimer of uracil and bromouracil (produced in irradiated frozen solution) have suggested a tentative explanation for the differences in products in the two organisms. The results for Enterococcus Stei appear consistent with the asumption that the major photo‐product of bromouracil is the dimer and this then decomposes to yield mainly uracil (as it does in vitro). E. coli B/r takes up less bromouracil and the photoproducts formed resemble more closely those found for the in vitro decomposition of the bromouracil‐uracil dimer. These results suggest that the primary photoproduct of bromouracil in E. coli B/r may be either a mixed dirner (intrastrand) with cytosine (with the subsequent deamination of the cytosine) or an interstrand crosslink with either bromouracil or cytosine. Thymine forms at least four photoproducts other than the dimer. Two of these photoproducts are significantly elevated in that portion of the bacterial DNA that is rendered non‐extractable by detergent after ultraviolet irradiation (remains associated with protein) and are also found in irradiated poly‐dAT. From the rate of formation of thymine dimers in irradiated (2537Å) E. coli B/r it can be calculated that approximately 1 erg/mm 2 produces one thymine dimer.