Rayko E, Goursot R
Laboratoire de Génétique Moléculaire, Institut Jacques Monod, Paris France.
Curr Genet. 1996 Jul 31;30(2):126-34. doi: 10.1007/s002940050111.
The mitochondrial (mt) genomes of three spontaneous cytoplasmic "palindromic" petite mutants of yeast were studied by restriction-enzyme analysis. These mt genomes were shown to be made up of an amplified "master basic unit" consisting of two inverted segments (a and A) and of two different unique segments (d and t) separating them. The basic unit was called "amphimeric", this term having been first proposed for certain lambda-phage mutants. We propose that in the mt genomes of the petite mutants studied, the four possible variants of the amphimeric basic unit form two - "flip" and "flop" - tetra-amphimeric repeat units datA-datA-DaTA-DaTA and DatA-DatA-daTA-daTA, respectively. These repeat units make two types of "amphimeric" mt genomes which exist in equal proportions in the cell. In each mt genome, the duplicated segment regularly alternates in its direct and inverted orientation (a...A...a...A...), whereas the unique segments are arranged twice in tandem fashion and twice in inverted fashion (d...d...D...D...d...d...andt...t...T...T...t...t...). The only difference between flip and flop amphimeric mt petite genomes is the different relative orientation of the unique segments in the mono-amphimers. In the mono-amphimers of flip mt genomes, both unique segments are arranged in the same direction (d...t and D...T), whereas in the mono-amphimers of flop mt genomes, both unique segments are arranged in opposite directions (D...t and d...T). Control experiments on one spontaneous petite mutant (which was an ancestor of the mutants studied here) and on three independent, previously investigated, EtBr-induced mutants showed that all of them were, in fact, organized in the same way. Analysing our experimental data and the results published by others, we conclude that amphimeric organization is a general feature of mt petite genomes of yeast previously called "palindromic" or "rearranged".
通过限制性酶切分析研究了酵母的三个自发细胞质“回文”小菌落突变体的线粒体（mt）基因组。这些线粒体基因组由一个扩增的“主要基本单元”组成，该单元由两个反向片段（a和A）以及将它们隔开的两个不同的独特片段（d和t）组成。这个基本单元被称为“双联体”，该术语最初是针对某些λ噬菌体突变体提出的。我们提出，在所研究的小菌落突变体的线粒体基因组中，双联体基本单元的四种可能变体分别形成两种——“翻转”和“扑通”——四双联体重复单元datA-datA-DaTA-DaTA和DatA-DatA-daTA-daTA。这些重复单元构成了两种类型的“双联体”线粒体基因组，它们在细胞中以相等的比例存在。在每个线粒体基因组中，重复片段以其正向和反向方向有规律地交替（a...A...a...A...），而独特片段则以串联方式排列两次，以反向方式排列两次（d...d...D...D...d...d...和t...t...T...T...t...t...）。翻转和扑通双联体线粒体小菌落基因组之间的唯一区别在于单双联体中独特片段的相对方向不同。在翻转线粒体基因组的单双联体中，两个独特片段以相同方向排列（d...t和D...T），而在扑通线粒体基因组的单双联体中，两个独特片段以相反方向排列（D...t和d...T）。对一个自发小菌落突变体（它是这里所研究突变体的祖先）以及三个独立的、先前研究过的溴化乙锭诱导突变体进行的对照实验表明，事实上它们都是以相同的方式组织的。分析我们的实验数据和其他人发表的结果，我们得出结论，双联体组织是酵母线粒体小菌落基因组的一个普遍特征，这些基因组以前被称为“回文”或“重排”。
