Ohgaki Kippei, Kanki Tomotake, Fukuoh Atsushi, Kurisaki Hironori, Aoki Yoshimasa, Ikeuchi Masaki, Kim Sang Ho, Hamasaki Naotaka, Kang Dongchon
Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
J Biochem. 2007 Feb;141(2):201-11. doi: 10.1093/jb/mvm020. Epub 2006 Dec 13.
Mitochondrial transcription factor A (TFAM) contains a basic C-terminal tail which is essential for the promoter-specific transcription. TFAM is also a major component of a protein-mitochondrial DNA (mtDNA) complex, called nucleoid, as a non-specific DNA-binding protein. However, little is known about a role of the C-tail in the nucleoid. Overexpression of full-length TFAM decreased the amount of a D-loop form of mtDNA in cells, while overexpression of TFAM lacking its C-tail (TFAM-DeltaC) did not, suggesting that the C-tail is involved in destabilization or formation of the D-loop. An mRNA for mtDNA-derived ND1 was hardly decreased in the former but rather decreased in the latter. Given that the D-loop formation is coupled with the transcription, the decrease in the D-loop is likely due to its destabilization. The recombinant full-length TFAM much strongly unwound DNA than TFAM-DeltaC, which is consistent with the above idea because D-loop is resolved by unwinding of the supercoiling state. Notably, truncation of the C-tail decreased DNA-binding activity of TFAM by three orders of magnitude. Thus, the C-terminal tail of TFAM is important for the strong general binding to mtDNA. This strong DNA-binding conferred by the C-tail may play an important role in the nucleoid structure.
线粒体转录因子A（TFAM）含有一个基本的C末端尾巴，这对于启动子特异性转录至关重要。TFAM作为一种非特异性DNA结合蛋白，也是一种称为类核的蛋白质-线粒体DNA（mtDNA）复合物的主要成分。然而，关于C末端尾巴在类核中的作用知之甚少。全长TFAM的过表达降低了细胞中mtDNA的D环形式的量，而缺乏其C末端尾巴的TFAM（TFAM-DeltaC）的过表达则没有，这表明C末端尾巴参与了D环的不稳定或形成。mtDNA衍生的ND1的mRNA在前一种情况下几乎没有减少，而在后一种情况下则减少。鉴于D环的形成与转录相关，D环的减少可能是由于其不稳定。重组全长TFAM比TFAM-DeltaC更强烈地解开DNA，这与上述观点一致，因为D环通过超螺旋状态的解开而被解析。值得注意的是，C末端尾巴的截断使TFAM的DNA结合活性降低了三个数量级。因此，TFAM的C末端尾巴对于与mtDNA的强普遍结合很重要。由C末端尾巴赋予的这种强DNA结合可能在类核结构中起重要作用。
