Tomkinson A E, Bonk R T, Kim J, Bartfeld N, Linn S
Department of Biochemistry, University of California, Berkeley 94720.
Nucleic Acids Res. 1990 Feb 25;18(4):929-35. doi: 10.1093/nar/18.4.929.
Mitochondrial forms of uracil DNA glycosylase and UV endonuclease have been purified and characterized from the mouse plasmacytoma cell line, MPC-11. As in other cell types, the mitochondrial uracil DNA glycosylase has properties very similar to those of the nuclear enzyme, although in this case the mitochondrial activity was also distinguishable by extreme sensitivity to dilution. Three mitochondrial UV endonuclease activities are also similar to nuclear enzymes; however, the relative amounts of these enzyme activities in the mitochondria is significantly different from that in the nucleus. In particular, mitochondria contain a much higher proportion of an activity analogous to UV endonuclease III. Nuclear UV endonuclease III activity is absent from XP group D fibroblasts and XP group D lymphoblasts have reduced, but detectable levels of the mitochondrial form of this enzyme. This residual activity differs in its properties from the normal mitochondrial form of UV endonuclease III, however. The presence of these enzyme activities which function in base excision repair suggests that such DNA repair occurs in mitochondria. Alternatively, these enzymes might act to mark damaged mitochondrial genomes for subsequent degradation.
从小鼠浆细胞瘤细胞系MPC-11中纯化并鉴定了尿嘧啶DNA糖基化酶和紫外线核酸内切酶的线粒体形式。与其他细胞类型一样，线粒体尿嘧啶DNA糖基化酶的特性与核酶非常相似，不过在这种情况下，线粒体活性对稀释极为敏感，这也使其具有可区分性。三种线粒体紫外线核酸内切酶活性也与核酶相似；然而，这些酶活性在线粒体中的相对含量与细胞核中的显著不同。特别是，线粒体中含有比例高得多的类似于紫外线核酸内切酶III的活性。XP D组成纤维细胞中不存在核紫外线核酸内切酶III活性，而XP D组淋巴母细胞中该酶的线粒体形式含量降低，但仍可检测到。然而，这种残余活性的特性与正常线粒体形式的紫外线核酸内切酶III不同。这些在碱基切除修复中起作用的酶活性的存在表明，此类DNA修复在线粒体中发生。或者，这些酶可能起到标记受损线粒体基因组以便随后降解的作用。
