Oda Kaoru, Kawasaki Nami, Fukuyama Masashi, Ikeda Shogo
Department of Biochemistry, Faculty of Science, Okayama University of Science, 1-1 Ridaicho, Okayama 700-0005, Japan.
J Biochem Mol Biol. 2007 Nov 30;40(6):1095-9. doi: 10.5483/bmbrep.2007.40.6.1095.
Endonuclease G (EndoG) is a mitochondrial non-specific nuclease that is highly conserved among the eukaryotes. Although the precise role of EndoG in mitochondria is not yet known, the enzyme is released from the mitochondria and digests nuclear DNA during apoptosis in mammalian cells. Schizosaccharomyces pombe has an EndoG homolog Pnu1p (previously named SpNuc1) that is produced as a precursor protein with a mitochondrial targeting sequence. During the sorting into mitochondria the signal sequence is cleaved to yield the functionally active endonuclease. From the analogy to EndoG, active extramitochondrial Pnu1p may trigger cell killing by degrading nuclear DNA. Here, we tested this possibility by expressing a truncated Pnu1p lacking the signal sequence in the extramitochondrial region of pnu1-deleted cells. The truncated Pnu1p was localized in the cytosol and nuclei of yeast cells. And ectopic expression of active Pnu1p led to cell death with fragmentation of nuclear DNA. This suggests that the Pnu1p is possibly involved in a certain type of yeast cell death via DNA fragmentation. Although expression of human Bak in S. pombe was lethal, Pnu1p nuclease is not necessary for hBak-induced cell death.
核酸内切酶G（EndoG）是一种线粒体非特异性核酸酶，在真核生物中高度保守。尽管EndoG在线粒体中的精确作用尚不清楚，但在哺乳动物细胞凋亡过程中，该酶会从线粒体中释放出来并消化核DNA。粟酒裂殖酵母有一种EndoG同源物Pnu1p（以前称为SpNuc1），它以前体蛋白的形式产生，带有线粒体靶向序列。在分选到线粒体的过程中，信号序列被切割，产生功能活性核酸内切酶。从与EndoG的类比来看，活性线粒体外Pnu1p可能通过降解核DNA引发细胞死亡。在这里，我们通过在缺失pnu1的细胞的线粒体外区域表达缺少信号序列的截短Pnu1p来测试这种可能性。截短的Pnu1p定位于酵母细胞的细胞质和细胞核中。活性Pnu1p的异位表达导致细胞死亡，并伴有核DNA片段化。这表明Pnu1p可能通过DNA片段化参与某种类型的酵母细胞死亡。尽管人Bak在粟酒裂殖酵母中的表达是致死性的，但Pnu1p核酸酶对于hBak诱导的细胞死亡不是必需的。
