The Mutagenicity of Thymidine Glycol in Escherichia coli Is Increased When It Is Part of a Tandem Lesion
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- 作者：Haidong Huang ; Shuhei Imoto ; Marc M. Greenberg
- 刊名：Biochemistry
- 出版年：2009
- 出版时间：August 25, 2009
- 年：2009
- 卷：48
- 期：33
- 页码：7833-7841
- 全文大小：861K
- 年卷期：v.48,no.33(August 25, 2009)
- ISSN：1520-4995
文摘
Tandem lesions are comprised of two contiguously damaged nucleotides. Tandem lesions make up the major family of reaction products generated from a pyrimidine nucleobase radical, which are formed in large amounts by ionizing radiation. One of these tandem lesions contains a thymidine glycol lesion flanked on its 5′-side by 2-deoxyribonolactone (LTg). The replication of this tandem lesion was investigated in Escherichia coli using single-stranded genomes. LTg is a much more potent replication block than thymidine glycol and is bypassed only under SOS-induced conditions. The adjacent thymidine glycol does not significantly affect nucleotide incorporation opposite 2-deoxyribonolactone in wild-type cells. In contrast, the misinsertion frequency opposite thymidine glycol, which is negligible in the absence of 2-deoxyribonolactone, increases to 10% in wild-type cells when LTg is flanked by a 3′-dG. Experiments in which the flanking nucleotides are varied and in cells lacking one of the SOS-induced bypass polymerases indicate that the mutations are due to a mechanism in which the primer misaligns prior to bypassing the lesion, which allows for an additional nucleotide to be incorporated across from the 3′-flanking nucleotide. Subsequent realignment and extension results in the observed mutations. DNA polymerases II and IV are responsible for misalignment induced mutations and compete with DNA polymerase V which reads through the tandem lesion. These experiments reveal that incorporation of the thymidine glycol into a tandem lesion indirectly induces increases in mutations by blocking replication, which enables the misalignment−realignment mechanism to compete with direct bypass by DNA polymerase V.