Lang B F, Cedergren R, Gray M W
Département de Biochimie, Université de Montréal, Québec, Canada.
Eur J Biochem. 1987 Dec 15;169(3):527-37. doi: 10.1111/j.1432-1033.1987.tb13641.x.
The DNA sequence of the mitochondrial large subunit (LSU) rRNA gene of Schizosaccharomyces pombe has been determined. In the direction of transcription, this gene is located between the gene coding for subunit II of cytochrome oxidase and a cluster of three tRNA genes. Both the 5' and 3' ends of the LSU rRNA have been mapped precisely: whereas the 5' end can be assigned unambiguously to a single nucleotide position, multiple 3' ends occur within a run of eight U residues. Based on these results, the S. pombe LSU rRNA is between 2818 and 2826 nucleotides long. A sequence motif immediately upstream of the 5' end of the gene resembles that of the mitochondrial promoter motif of Saccharomyces cerevisiae; however, the sequence at the 3' end of the gene is not similar to any of the motifs implicated as processing signals in other mitochondrial systems. Unlike its counterparts in S. cerevisiae and Aspergillus nidulans, the mitochondrial LSU rRNA gene of S. pombe does not contain an intron. Comparison of potential secondary structure among the three fungal mitochondrial and Escherichia coli LSU rRNAs has defined a common secondary structure core, held together by long-range hydrogen-bonding interactions. A 5.8S-like structure is present within the 5'-terminal region of all three fungal mitochondrial LSU rRNAs; in contrast, no 4.5S-like structure is evident at the 3' end of these molecules. An evolutionary evaluation of highly conserved regions of a small set of LSU rRNA sequences suggests that S. pombe mitochondria diverged from a mitochondrial proto-fungal branch earlier than either A. nidulans or S. cerevisiae mitochondria. This result, considered in conjunction with the patterns of genome organization and codon usage in fungal mitochondria, points to a slower evolutionary clock speed in the mitochondrial genome of S. pombe.
粟酒裂殖酵母线粒体大亚基（LSU）rRNA基因的DNA序列已被测定。在转录方向上，该基因位于细胞色素氧化酶亚基II的编码基因与三个tRNA基因簇之间。LSU rRNA的5'端和3'端均已精确定位：5'端可明确地定位到单个核苷酸位置，而多个3'端出现在连续八个U残基中。基于这些结果，粟酒裂殖酵母LSU rRNA的长度在2818至2826个核苷酸之间。该基因5'端上游紧邻的序列基序类似于酿酒酵母的线粒体启动子基序；然而，该基因3'端的序列与其他线粒体系统中作为加工信号的任何基序均不相似。与酿酒酵母和构巢曲霉中的对应基因不同，粟酒裂殖酵母的线粒体LSU rRNA基因不含内含子。对三种真菌线粒体和大肠杆菌LSU rRNA潜在二级结构的比较确定了一个共同的二级结构核心，该核心通过长程氢键相互作用维系在一起。在所有三种真菌线粒体LSU rRNA的5'端区域均存在一个类似5.8S的结构；相反，在这些分子的3'端没有明显的类似4.5S的结构。对一小部分LSU rRNA序列高度保守区域的进化评估表明，粟酒裂殖酵母线粒体比构巢曲霉或酿酒酵母线粒体更早地从线粒体原始真菌分支中分化出来。结合真菌线粒体基因组组织模式和密码子使用情况来考虑这一结果，表明粟酒裂殖酵母线粒体基因组的进化时钟速度较慢。
