Gillum A M, Clayton D A
Proc Natl Acad Sci U S A. 1978 Feb;75(2):677-81. doi: 10.1073/pnas.75.2.677.
The single-stranded mitochondrial DNA (mtDNA) displacement-loop initiation sequence (7S mtDNA) is hydrogen-bonded at the origin of replication in animal cell mtDNA. Analysis of 7S mtDNA from several cell sources indicates that this initiation sequence exists as a family of fragments of relatively discrete lengths. mtDNA from both mouse L cells and mouse liver has four major sizes of 7S mtDNA fragments, ranging from 500 to 580 nucleotides in length. The 5'-end region of each of these species is the same; thus, the size heterogeneity is due primarily to differences in length at the 3'-end of these molecules. By contrast, 7S mtDNA from both human KB cells and human liver exists in three major forms, ranging from 555 to 615 nucleotides in length, due to differences at both terminal regions. The mtDNA initiation sequence from Xenopus laevis oocytes also exists in at least two forms, 1350 and 1510 nucleotides in length. Thus, the maintenance of multiple forms of mtDNA initiation sequence appears to be a general phenomenon of animal cells, although the precise mechanism of synthesis or processing of these forms is variable. The sequence of 42 nucleotides at the 5'-end of 7S mtDNA from mouse L cells has been determined and found to be rich in dGuo and dThd residues, with no apparent palindromes or potential secondary structures. We thus present sequence information on the replication origin of mtDNA, as defined by the naturally occurring 7S mtDNA.
单链线粒体DNA（mtDNA）置换环起始序列（7S mtDNA）在动物细胞mtDNA的复制起点处形成氢键。对来自多种细胞来源的7S mtDNA的分析表明，该起始序列以一系列长度相对离散的片段形式存在。来自小鼠L细胞和小鼠肝脏的mtDNA有四种主要大小的7S mtDNA片段，长度在500至580个核苷酸之间。这些片段的5'端区域相同；因此，大小异质性主要是由于这些分子3'端长度的差异。相比之下，来自人类KB细胞和人类肝脏的7S mtDNA以三种主要形式存在，长度在555至615个核苷酸之间，这是由于两个末端区域都存在差异。非洲爪蟾卵母细胞的mtDNA起始序列也至少以两种形式存在，长度分别为1350和1510个核苷酸。因此，多种形式的mtDNA起始序列的存在似乎是动物细胞的普遍现象，尽管这些形式的合成或加工的确切机制各不相同。已确定小鼠L细胞7S mtDNA 5'端的42个核苷酸序列，发现其富含dGuo和dThd残基，没有明显的回文结构或潜在的二级结构。因此，我们提供了由天然存在的7S mtDNA定义的mtDNA复制起点的序列信息。
