Drouin G, Moniz de Sá M, Zuker M
Department of Biology, University of Ottawa, ON, Canada.
J Mol Evol. 1995 Dec;41(6):841-9. doi: 10.1007/BF00173163.
The single-copy actin gene of Giardia lamblia lacks introns; it has an average of 58% amino acid identity with the actin of other species; and 49 of its amino acids can be aligned with the amino acids of a consensus sequence of heat shock protein 70. Analysis of the potential RNA secondary structure in the transcribed region of the G. lamblia actin gene and of the single-copy actin gene of nine other species did not reveal any conserved structures. The G. lamblia actin sequence was used to root the phylogenetic trees based on 65 actin protein sequences from 43 species. This tree is congruent with small-subunit rRNA trees in that it shows that oomycetes are not related to higher fungi; that kineto-platid protozoans, green plants, fungi and animals are monophyletic groups; and that the animal and fungal lineages share a more recent common ancestor than either does with the plant lineage. In contrast to small-subunit rRNA trees, this tree shows that slime molds diverged after the plant lineage. The slower rate of evolution of actin genes of slime molds relative to those of plants, fungi, and animals species might be responsible for this incongruent branching.
蓝氏贾第鞭毛虫的单拷贝肌动蛋白基因没有内含子；它与其他物种的肌动蛋白平均有58%的氨基酸同一性；并且其49个氨基酸可与热休克蛋白70的共有序列的氨基酸比对。对蓝氏贾第鞭毛虫肌动蛋白基因转录区域以及其他九个物种的单拷贝肌动蛋白基因的潜在RNA二级结构分析未发现任何保守结构。基于来自43个物种的65个肌动蛋白蛋白质序列构建系统发育树时，使用了蓝氏贾第鞭毛虫的肌动蛋白序列作为根。这棵树与小亚基rRNA树一致，因为它表明卵菌与高等真菌无关；动质体原生动物、绿色植物、真菌和动物是单系类群；并且动物和真菌谱系共享的共同祖先比它们与植物谱系的共同祖先更近。与小亚基rRNA树不同的是，这棵树表明黏菌在植物谱系之后分化。黏菌肌动蛋白基因相对于植物、真菌和动物物种的肌动蛋白基因进化速度较慢，这可能是造成这种不一致分支的原因。
