Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China.
Eur J Protistol. 2013 Jan;49(1):40-9. doi: 10.1016/j.ejop.2012.05.001. Epub 2012 Jun 9.
Polyubiquitin genes from seven ciliate species were amplified, cloned and sequenced. It is estimated that Strombidium sulcatum, Euplotes vannus, E. rariseta and Anteholosticha manca have a polyubiquitin gene of 3 repeats, and A. parawarreni, Paramecium caudatum and Pseudokeronopsis flava 4 repeats. The newly obtained ubiquitins mostly differ from that of humans by 1-5 residues in amino acid sequences. A neighbor-joining tree constructed based on monomeric ubiquitin genes supports the monophyly of an assemblage comprising the litostomateans and some oligohymenophoreans, but not the class Spirotrichea. The monomers from the same species are generally placed together and highly supported for the class Litostomatea, the genera Paramecium and Ichthyophthirius, but not for other species. The non-synonymous/synonymous rate ratio (dN/dS) at the protein level are less than 1, and the synonymous nucleotide differences per synonymous site (p(S)) from intraspecific comparisons are fairly high (0.02-0.72). These results indicate that ciliates have not only the conserved, but also some quite divergent, polyubiquitin genes and confirm that the polyubiquitin genes in ciliates evolve according to the birth-and-death mode of evolution under strong purifying selection.
从 7 种纤毛虫中扩增、克隆和测序了多聚泛素基因。据估计，Strombidium sulcatum、Euplotes vannus、E. rariseta 和 Anteholosticha manca 具有 3 个重复的多聚泛素基因，而 A. parawarreni、Paramecium caudatum 和 Pseudokeronopsis flava 具有 4 个重复。新获得的泛素在氨基酸序列上与人类的差异大多为 1-5 个残基。基于单体泛素基因构建的邻接树支持包括 litostomateans 和一些 oligohymenophoreans 的集合的单系性，但不支持 Spirotrichea 类。来自同一物种的单体通常一起放置，并高度支持 Litostomatea 类、Paramecium 和 Ichthyophthirius 属，但不支持其他物种。蛋白质水平上的非同义/同义比率 (dN/dS) 小于 1，并且从种内比较来看，同义核苷酸差异 (p(S)) 相当高（0.02-0.72）。这些结果表明纤毛虫不仅具有保守的，而且具有一些相当不同的多聚泛素基因，并证实纤毛虫中的多聚泛素基因根据强烈纯化选择下的生死进化模式进化。
