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INDEPENDENCE OF PHOTOPRODUCT FORMATION ON DNA CONFORMATION *
Author(s) -
Patrick Michael H.,
Gray Donald M.
Publication year - 1976
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.1751-1097.1976.tb06867.x
Subject(s) - chemistry , dna , adduct , thymine , ethanol , stereochemistry , circular dichroism , pyrimidine , conformational change , native state , pyrimidine dimer , crystallography , photochemistry , biochemistry , dna damage , organic chemistry
— In an ethanolic solution native T7 DNA can undergo conformational transitions from the B conformation (0% ethanol) to the C‐like (60% w/w ethanol) and the A (80% w/w ethanol) conformations. We have investigated the formation of three classes of thymine‐derived photoproducts in T7 DNA irradiated (280 nm) in the B, C‐like, and A conformations, which were monitored by circular dichroism measurements. We find that the predominant class of thymine‐derived photoproducts in any conformational state is cyclobutyl dipyrimidines. While the ‘spore product,’ 5‐thyminyl‐5,6‐dihydrothymine, which belongs to another class of photoproductsf does form in native DNA in the A conformation, its yield in denatured DNA at 80% ethanol is the same as that in native DNA. The yield of pyrimidine adduct, a third photoproduct class, is a maximum at 50–60% ethanol. This effect of ethanol is probably not due to the ethanol‐induced C‐like conformation, however, since pyrimidine adduct formation is not enhanced when T7 DNA is irradiated in the C conformation in 6 M CsCl or in intact phage. We conclude from these and other data in the literature that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproducts will form in native DNA.