期刊
MOLECULAR AND CELLULAR BIOLOGY
卷 34, 期 12, 页码 2176-2187出版社
AMER SOC MICROBIOLOGY
DOI: 10.1128/MCB.01452-13
关键词
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资金
- Ligue contre le Cancer (Equipe Labelisee)
- Fondation Princesse Grace
- Ecole Normale Superieure
- Ligue Nationale contre le Cancer
A/T mutations at immunoglobulin loci are introduced by DNA polymerase eta (Pol eta) during an Msh2/6-dependent repair process which results in A's being mutated 2-fold more often than T's. This patch synthesis is initiated by a DNA incision event whose origin is still obscure. We report here the analysis of A/T oligonucleotide mutation substrates inserted at the heavy chain locus, including or not including internal C's or G's. Surprisingly, the template composed of only A's and T's was highly mutated over its entire 90-bp length, with a 2-fold decrease in mutation from the 5' to the 3' end and a constant A/T ratio of 4. These results imply that Pol eta synthesis was initiated from a break in the 5'-flanking region of the substrate and proceeded over its entire length. The A/T bias was strikingly altered in an Ung(-/-) background, which provides the first experimental evidence supporting a concerted action of Ung and Msh2/6 pathways to generate mutations at A/T bases. New analysis of Pms2(-/-) animals provided a complementary picture, revealing an A/T mutation ratio of 4. We therefore propose that Ung and PMs2 may exert a mutual backup function for the DNA incision that promotes synthesis by Pol eta, each with a distinct strand bias.
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