Herbert C J, Dujardin G, Labouesse M, Slonimski P P
Centre de Génétique Moléculaire du CNRS, Laboratoire propre associé à l'Université Pierre et Marie Curie, Gif-sur-Yvette, France.
Mol Gen Genet. 1988 Aug;213(2-3):297-309. doi: 10.1007/BF00339595.
We studied the NAM2 genes of Saccharomyces douglasii and Saccharomyces cerevisiae, and showed that they are interchangeable for all the known functions of these genes, both mitochondrial protein synthesis and mitochondrial mRNA splicing. This confirms the prediction that the S. douglasii NAM2D gene encodes the mitochondrial leucyl tRNA synthetase (EC 6.1.1.4.). The observation that these enzymes are interchangeable for their mRNA splicing functions, even though there are significant differences in the intron/exon structure of their mitochondrial genome, suggests that they may have a general role in yeast mitochondrial RNA splicing. A short open reading frame (ORF) precedes the synthetase-encoding ORF, and we showed that at least in S. cerevisiae this is not essential for the expression of the gene; however, it may be involved in a more subtle type of regulation. Sequence comparisons of S. douglasii and S. cerevisiae revealed a particularly interesting situation from the evolutionary point of view. It appears that the two yeasts have diverged relatively recently: there is remarkable nucleotide sequence conservation, with no deletions or insertions, but numerous (albeit non-saturating) silent substitutions resulting from transitions. This applies not only to the NAM2 coding regions, but also to two other ORFs flanking the NAM2 ORF. The regions between the ORFs (believed to be intergenic regions) are much less conserved, with several deletions and insertions. Thus S. douglasii and S. cerevisiae provide an ideal system for the study of molecular evolution, being two yeasts "caught in the act" of speciation.
我们研究了道格拉斯酿酒酵母和酿酒酵母的NAM2基因，结果表明，对于这些基因的所有已知功能，包括线粒体蛋白质合成和线粒体mRNA剪接，它们都是可互换的。这证实了以下预测：道格拉斯酿酒酵母的NAM2D基因编码线粒体亮氨酰tRNA合成酶（EC 6.1.1.4.）。尽管它们线粒体基因组的内含子/外显子结构存在显著差异，但这些酶在mRNA剪接功能上是可互换的，这一观察结果表明它们可能在酵母线粒体RNA剪接中具有普遍作用。在编码合成酶的开放阅读框（ORF）之前有一个短的开放阅读框，我们发现至少在酿酒酵母中，这对该基因的表达不是必需的；然而，它可能参与一种更微妙的调控类型。从进化的角度来看，道格拉斯酿酒酵母和酿酒酵母之间的序列比较揭示了一种特别有趣的情况。这两种酵母似乎是在相对较近的时间分化的：核苷酸序列有显著的保守性，没有缺失或插入，但有许多（尽管未达到饱和）由转换导致的沉默替代。这不仅适用于NAM2编码区，也适用于NAM2 ORF两侧的另外两个ORF。ORF之间的区域（被认为是基因间区域）保守性要低得多，有几个缺失和插入。因此，道格拉斯酿酒酵母和酿酒酵母为分子进化研究提供了一个理想的系统，是处于物种形成“过程中”的两种酵母。
