Alkali-labile photolesions mapping to purine sites in ultraviolet-irradiated DNA.
Gel sequencing experiments with the 5'- and 3'-end-labeled oligonucleotides d(A3GA4GA5GA6GA3G) and d(AT)10 have demonstrated that dimeric adenine photoproducts and thymine-adenine photoadducts constitute alkali-labile lesions in UV-irradiated DNA. On treatment with hot piperidine, DNA strand breakage occurs predominantly at the sites of 5'-adenines in the dimeric photoproducts and of 3'-adenines in the thymine-adenine photoadducts. With 5'-end-labeled oligonucleotides of mixed sequence, major UV-induced loci for alkaline cleavage map to purine bases flanked on their 5'-side by two pyrimidines. This behavior does not arise from enhanced photoreactivity of purines in this sequence context as has been inferred from photofootprinting studies. Instead, as shown by 3'-labeling and selective substitution with 5-methylcytosine, it results from the anomalous electrophoretic mobility of 5'-end-labeled fragments produced by alkaline cleavage of DNA at adjacent pyrimidine (6-4) pyrimidone photoproducts.
Hejmadi
V
V
Division of Biochemistry, Queen's University, Belfast, Northern Ireland.
Stevenson
C
C
Kumar
S
S
Davies
R J
RJ
D000468:Alkalies; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D004249:DNA Damage; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009705:Nucleosides / Q000737:chemistry / Q000528:radiation effects; D010777:Photochemistry; D011687:Purines / Q000737:chemistry; D014466:Ultraviolet Rays
D000468:Alkalies; D009705:Nucleosides; D011687:Purines; C028270:dinucleoside dimers; D004247:DNA