Kaguni L S, Olson M W
Department of Biochemistry, Michigan State University, East Lansing 48824.
Proc Natl Acad Sci U S A. 1989 Sep;86(17):6469-73. doi: 10.1073/pnas.86.17.6469.
The mitochondrial DNA polymerase from Drosophila embryos lacks dNTP turnover activity. However, a potent 3'----5' exonuclease activity can be detected by a specific assay in which the exonuclease excises mispaired nucleotides at the 3' termini of primed synthetic and natural DNA templates. The excision of a mispaired nucleotide occurs at a significantly greater rate than excision of a correctly paired nucleotide and, under conditions of DNA synthesis, hydrolysis of a mispaired terminal nucleotide occurs prior to primer extension. The 3'----5' exonuclease copurifies quantitatively with DNA polymerase gamma and cosediments with the nearly homogeneous enzyme under native conditions. These results suggest that the 3'----5' exonuclease provides a proofreading function to enhance the fidelity of DNA synthesis during Drosophila mitochondrial DNA replication.
果蝇胚胎中的线粒体DNA聚合酶缺乏脱氧核苷三磷酸（dNTP）周转活性。然而，通过一种特定检测方法可检测到一种强大的3'→5'核酸外切酶活性，在该检测中，核酸外切酶切除引发的合成DNA模板和天然DNA模板3'末端的错配核苷酸。错配核苷酸的切除速率明显高于正确配对核苷酸的切除速率，并且在DNA合成条件下，错配末端核苷酸的水解发生在引物延伸之前。3'→5'核酸外切酶与DNA聚合酶γ定量共纯化，并且在天然条件下与几乎纯的该酶一起沉降。这些结果表明，3'→5'核酸外切酶提供校对功能，以提高果蝇线粒体DNA复制过程中DNA合成的保真度。
