Di Re M, Sembongi H, He J, Reyes A, Yasukawa T, Martinsson P, Bailey L J, Goffart S, Boyd-Kirkup J D, Wong T S, Fersht A R, Spelbrink J N, Holt I J
MRC-Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, CB2 0XY, UK.
Nucleic Acids Res. 2009 Sep;37(17):5701-13. doi: 10.1093/nar/gkp614. Epub 2009 Jul 22.
The accessory subunit of mitochondrial DNA polymerase gamma, POLGbeta, functions as a processivity factor in vitro. Here we show POLGbeta has additional roles in mitochondrial DNA metabolism. Mitochondrial DNA is arranged in nucleoprotein complexes, or nucleoids, which often contain multiple copies of the mitochondrial genome. Gene-silencing of POLGbeta increased nucleoid numbers, whereas over-expression of POLGbeta reduced the number and increased the size of mitochondrial nucleoids. Both increased and decreased expression of POLGbeta altered nucleoid structure and precipitated a marked decrease in 7S DNA molecules, which form short displacement-loops on mitochondrial DNA. Recombinant POLGbeta preferentially bound to plasmids with a short displacement-loop, in contrast to POLGalpha. These findings support the view that the mitochondrial D-loop acts as a protein recruitment centre, and suggest POLGbeta is a key factor in the organization of mitochondrial DNA in multigenomic nucleoprotein complexes.
线粒体DNA聚合酶γ的辅助亚基POLGβ在体外作为一种持续性因子发挥作用。在此我们表明，POLGβ在线粒体DNA代谢中还有其他作用。线粒体DNA排列在核蛋白复合物或类核中，类核通常包含线粒体基因组的多个拷贝。POLGβ的基因沉默增加了类核数量，而POLGβ的过表达则减少了线粒体类核的数量并增大了其尺寸。POLGβ表达的增加和减少均改变了类核结构，并导致形成线粒体DNA上短置换环的7S DNA分子显著减少。与POLGα相反，重组POLGβ优先结合具有短置换环的质粒。这些发现支持线粒体D环作为蛋白质招募中心的观点，并表明POLGβ是多基因组核蛋白复合物中线粒体DNA组织的关键因子。
