Keeling P J, Doolittle W F
Department of Biochemistry, Dalhousie University, Nova Scotia, Canada.
Mol Biol Evol. 1996 Dec;13(10):1297-305. doi: 10.1093/oxfordjournals.molbev.a025576.
The tubulin gene family, which includes alpha-,beta-, and gamma-tubulin subfamilies, is composed of highly conserved proteins which are the principle structural and functional components of eukaryotic microtubules. We are interested in (1) establishing when in eukaryotic evolution the duplications leading to paralogous alpha, beta, and gamma subfamilies occurred and (2) the possible utility of tubulin sequences in reconstructing organismal phylogeny. To broaden the taxonomic representation of alpha-tubulins so that it roughly equals that of beta-tubulins, alpha-tubulin genes from three Microsporidia (Encephalitozoon hellem, Nosema locustae, and Spraguea lophii), two Parabasalia (Monocercomonas sp. and Trichomitus batrachorum), and one Heterolobosean (Acrasis rosea) were sequenced. With these new genes, phylogenetic trees of alpha- and beta-tubulins were constructed and compared. Trees were congruent with each other, but incongruent with other molecular phylogenies. The agreement between alpha- and beta-tubulin trees could arise by the co-adaptation of one molecule to variants of the other as a result of their intimate steric association in microtubules. Thus, these trees may not be providing independent support for the phylogenetic results. However, one of these unexpected results, that microsporidia cluster with fungi, is supported by other circumstantial evidence, and may therefore reflect a real relationship despite the basal position usually assigned to microsporidia. Relationships between the three tubulins were also examined by constructing trees of all three types. These trees were found to be of limited value for determining the position of the root within each subfamily because of the great interfamily distances, but they do confirm the classification of all known genes into three monophyletic subfamilies. Divergent genes from Caenorhabditis elegans and Saccharomyces cerevisiae that have been proposed to represent the novel classes delta- and epsilon-tubulin were found to be specifically related to gamma-tubulins from animals and fungi respectively, and therefore are best seen as rapidly evolving orthologues of gamma-tubulin.
微管蛋白基因家族包括α-、β-和γ-微管蛋白亚家族，由高度保守的蛋白质组成，这些蛋白质是真核生物微管的主要结构和功能成分。我们感兴趣的是：（1）确定在真核生物进化过程中，导致同源α、β和γ亚家族的复制发生在何时；（2）微管蛋白序列在重建生物系统发育中的可能用途。为了拓宽α-微管蛋白的分类代表性，使其大致与β-微管蛋白的相等，对来自三种微孢子虫（海伦脑炎微孢子虫、蝗虫微孢子虫和蛙片虫微孢子虫）、两种副基体生物（单鞭滴虫属和蛙三毛滴虫）以及一种异叶足虫（玫瑰集胞菌）的α-微管蛋白基因进行了测序。利用这些新基因，构建并比较了α-和β-微管蛋白的系统发育树。这些树彼此一致，但与其他分子系统发育不一致。α-和β-微管蛋白树之间的一致性可能是由于一个分子与另一个分子的变体共同适应，这是由于它们在微管中紧密的空间关联。因此，这些树可能无法为系统发育结果提供独立支持。然而，这些意外结果之一，即微孢子虫与真菌聚类，得到了其他间接证据的支持，因此尽管微孢子虫通常被置于基部位置，但这可能反映了一种真实的关系。还通过构建所有三种类型的树来研究三种微管蛋白之间的关系。由于家族间距离很大，这些树在确定每个亚家族内根部位置方面价值有限，但它们确实证实了所有已知基因可分为三个单系亚家族。来自秀丽隐杆线虫和酿酒酵母的已被提议代表新的δ-和ε-微管蛋白类别的分歧基因，分别被发现与动物和真菌的γ-微管蛋白特别相关，因此最好被视为γ-微管蛋白快速进化的直系同源物。
