Campbell C L, Thorsness P E
Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 82071-3944, USA.
J Cell Sci. 1998 Aug;111 ( Pt 16):2455-64. doi: 10.1242/jcs.111.16.2455.
Inactivation of Yme1p, a mitochondrially-localized ATP-dependent metallo-protease in the yeast Saccharomyces cerevisiae, causes a high rate of DNA escape from mitochondria to the nucleus as well as pleiotropic functional and morphological mitochondrial defects. The evidence presented here suggests that the abnormal mitochondria of a yme1 strain are degraded by the vacuole. First, electron microscopy of Yme1p-deficient strains revealed mitochondria physically associated with the vacuole via electron dense structures. Second, disruption of vacuolar function affected the frequency of mitochondrial DNA escape from yme1 and wild-type strains. Both PEP4 or PRC1 gene disruptions resulted in a lower frequency of mitochondrial DNA escape. Third, an in vivo assay that monitors vacuole-dependent turnover of the mitochondrial compartment demonstrated an increased rate of mitochondrial turnover in yme1 yeast when compared to the rate found in wild-type yeast. In this assay, vacuolar alkaline phosphatase, encoded by PHO8, was targeted to mitochondria in a strain bearing disruption to the genomic PHO8 locus. Maturation of the mitochondrially localized alkaline phosphatase pro-enzyme requires proteinase A, which is localized in the vacuole. Therefore, alkaline phosphatase activity reflects vacuole-dependent turnover of mitochondria. This assay reveals that mitochondria of a yme1 strain are taken up by the vacuole more frequently than mitochondria of an isogenic wild-type strain when these yeast are cultured in medium necessitating respiratory growth. Degradation of abnormal mitochondria is one pathway by which mitochondrial DNA escapes and migrates to the nucleus.
Yme1p是酿酒酵母中一种定位于线粒体的ATP依赖性金属蛋白酶，Yme1p的失活会导致DNA从线粒体大量逃逸到细胞核，同时引发线粒体多效性功能和形态缺陷。本文提供的证据表明，yme1菌株的异常线粒体被液泡降解。首先，对缺乏Yme1p的菌株进行电子显微镜观察发现，线粒体通过电子致密结构与液泡发生物理关联。其次，液泡功能的破坏影响了线粒体DNA从yme1菌株和野生型菌株逃逸的频率。PEP4或PRC1基因的破坏均导致线粒体DNA逃逸频率降低。第三，一项监测线粒体区室液泡依赖性周转的体内试验表明，与野生型酵母相比，yme1酵母中线粒体周转速率增加。在该试验中，由PHO8编码的液泡碱性磷酸酶在基因组PHO8位点发生破坏的菌株中靶向定位于线粒体。定位于线粒体的碱性磷酸酶原酶的成熟需要蛋白酶A，而蛋白酶A定位于液泡中。因此，碱性磷酸酶活性反映了线粒体的液泡依赖性周转。该试验表明，当这些酵母在需要呼吸生长的培养基中培养时，yme1菌株的线粒体比同基因野生型菌株的线粒体更频繁地被液泡摄取。异常线粒体的降解是线粒体DNA逃逸并迁移到细胞核的一条途径。
