Mechanism of SOS mutagenesis of UV-irradiated DNA: mostly error-free processing of deaminated cytosine.
We measured the kinetics of growth and mutagenesis of UV-irradiated DNA of phages S13 and lambda that were undergoing SOS repair; the kinetics strongly suggest that most of SOS mutagenesis arises from the deamination of cytosine in cyclobutane pyrimidine dimers, producing C----T transitions. This occurs because the SOS mechanism bypasses T--T dimers promptly, while bypass of cytosine-containing dimers is delayed long enough for deamination to occur. The mutations are thus primarily the product of a faithful mechanism of lesion bypass by a DNA polymerase and are not, as had been generally thought, the product of an error-prone mechanism. All of these observations are explained by the A-rule, which is that adenine nucleotides are inserted noninstructionally opposite DNA lesions.
Tessman
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I
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907.
Liu
S K
SK
Kennedy
M A
MA
D003596:Cytosine / Q000378:metabolism*; D004249:DNA Damage; D004279:DNA, Viral / Q000528:radiation effects*; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects; D016296:Mutagenesis; D011740:Pyrimidine Dimers; D013014:SOS Response, Genetics; D013997:Time Factors; D014466:Ultraviolet Rays
D004279:DNA, Viral; D011740:Pyrimidine Dimers; D003596:Cytosine