Amati B B, Goldschmidt-Clermont M, Wallace C J, Rochaix J D
Department of Molecular Biology, University of Geneva, Switzerland.
J Mol Evol. 1988;28(1-2):151-60. doi: 10.1007/BF02143507.
We have isolated complementary DNA (cDNA) clones for apocytochrome c from the green alga Chlamydomonas reinhardtii and shown that they are encoded by a single nuclear gene termed cyc. Cyc mRNA levels are found to depend primarily on the presence of acetate as a reduced carbon source in the culture medium. The deduced amino acid sequence shows that, apart from the probable removal of the initiating methionine, C. reinhardtii apocytochrome c is synthesized in its mature form. Its structure is generally similar to that of cytochromes c from higher plants. Several punctual deviations from the general pattern of cytochrome c sequences that is found in other organisms have interesting structural and functional implications. These include, in particular, valines 19 and 39, asparagine 78, and alanine 83. A phylogenetic tree was constructed by the matrix method from cytochrome c data for a representative range of species. The results suggest that C. reinhardtii diverged from higher plants approximately 700-750 million years ago; they also are not easy to reconcile with the current attribution of Chlamydomonas reinhardtii and Enteromorpha intestinalis to a unique phylum, because these two species probably diverged from one another at about the same time as they diverged from the line leading to higher plants.
我们从莱茵衣藻这种绿藻中分离出了脱辅基细胞色素c的互补DNA（cDNA）克隆，并表明它们由一个名为cyc的单拷贝核基因编码。发现Cyc mRNA水平主要取决于培养基中作为还原碳源的乙酸盐的存在。推导的氨基酸序列表明，除了可能去除起始甲硫氨酸外，莱茵衣藻脱辅基细胞色素c是以其成熟形式合成的。其结构总体上与高等植物细胞色素c的结构相似。与其他生物体中发现的细胞色素c序列的一般模式存在的几个点突变具有有趣的结构和功能意义。这些尤其包括第19位和第39位的缬氨酸、第78位的天冬酰胺以及第83位的丙氨酸。通过矩阵法利用一系列代表性物种的细胞色素c数据构建了系统发育树。结果表明，莱茵衣藻大约在7亿至7.5亿年前与高等植物分化；它们也难以与目前将莱茵衣藻和肠浒苔归为一个独特门的分类相协调，因为这两个物种可能在与从导致高等植物的谱系分化的大致相同时间彼此分化。
