Haid A, Schweyen R J, Bechmann H, Kaudewitz F, Solioz M, Schatz G
Eur J Biochem. 1979 Mar;94(2):451-64. doi: 10.1111/j.1432-1033.1979.tb12913.x.
Mitochondrial mutants of Saccharomyces cerevisiae defective in cytochrome b were analyzed genetically and biochemically in order to elucidate the role of the mitochondrial genetic system in the biosynthesis of this cytochrome. The mutants mapped between OLI1 and OLI2 on mitochondrial DNA in a region called COB. A fine structure map of the COB region was constructed by rho- deletion mapping and recombination analysis. The combined genetic and biochemical data indicate that the COB region is mosaic and contains at least five distinct clusters of mutants, A-E, with A being closest to OLI2 and E being closest to OLI1. Clusters A, C and E are probably coding regions for apocytochrome b, whereas clusters B and D seem to be involved in as yet unknown functions. These conclusions rest on the following evidence. 1. Most mutants in clusters A, C and E have specifically lost cytochrome b. Many of them accumulate smaller mitochondrial translation products; some of these were identified as fragments of apocytochrome b by proteolytic fingerprinting. The molecular weight of these fragments depends on the map position of the mutant, increasing in the direction OLI2 leads to OLI1. The mutant closest to OLI1 accumulates an apocytochrome b which is slightly larger than that of wild type. 2. A mutant in cluster C exhibits a spectral absorption band of cytochrome b that is shifted 1.5 nm to the red. 3. Mutants in clusters B and D are pleiotropic. A majority of them are conditional and lack the absorption bands of both cytochrome b and cytochrome aa3; these mutants also fail to accumulate apocytochrome b and subunit I of cytochrome c oxidase and instead form a large number of abnormal translation products whose nature is unknown. 4. Zygotic complementation tests reveal at least two complementation groups: The first group includes all mutants in cluster B and the second group includes mutants in clusters (A + C + D + E).
为了阐明线粒体遗传系统在细胞色素b生物合成中的作用，对酿酒酵母中细胞色素b有缺陷的线粒体突变体进行了遗传和生化分析。这些突变体在线粒体DNA上位于OLI1和OLI2之间一个名为COB的区域。通过ρ-缺失图谱分析和重组分析构建了COB区域的精细结构图。综合遗传和生化数据表明，COB区域是嵌合的，包含至少五个不同的突变体簇，A - E，其中A最靠近OLI2，E最靠近OLI1。簇A、C和E可能是脱辅基细胞色素b的编码区域，而簇B和D似乎参与尚未明确的功能。这些结论基于以下证据。1. 簇A、C和E中的大多数突变体特异性地失去了细胞色素b。其中许多积累了较小的线粒体翻译产物；通过蛋白水解指纹图谱分析，其中一些被鉴定为脱辅基细胞色素b的片段。这些片段的分子量取决于突变体的图谱位置，在从OLI2到OLI1的方向上增加。最靠近OLI1的突变体积累的脱辅基细胞色素b比野生型略大。2. 簇C中的一个突变体表现出细胞色素b的光谱吸收带向红移了1.5 nm。3. 簇B和D中的突变体具有多效性。它们中的大多数是条件性的，并且缺乏细胞色素b和细胞色素aa3的吸收带；这些突变体也不能积累脱辅基细胞色素b和细胞色素c氧化酶的亚基I，而是形成大量性质未知的异常翻译产物。4. 合子互补试验揭示了至少两个互补组：第一组包括簇B中的所有突变体，第二组包括簇（A + C + D + E）中的突变体。
