Katz Laura A, Bornstein Jacob G, Lasek-Nesselquist Erica, Muse Spencer V
Department of Biological Sciences, Smith College, Northampton, Massachusetts, USA.
Mol Biol Evol. 2004 Mar;21(3):555-62. doi: 10.1093/molbev/msh048. Epub 2003 Dec 23.
The accumulation of divergent histone H4 amino acid sequences within and between ciliate lineages challenges traditional views of the evolution of this essential eukaryotic protein. We analyzed histone H4 sequences from 13 species of ciliates and compared these data with sequences from well-sampled eukaryotic clades. Ciliate histone H4s differ from one another at as many as 46% of their amino acids, in contrast with the highly conserved character of this protein in most other eukaryotes. Equally striking, we find paralogs of histone H4 within ciliate genomes that differ by up to 25% of their amino acids, whereas paralogs in other eukaryotes share identical or nearly identical amino acid sequences. Moreover, the most divergent H4 proteins within ciliates are found in the lineages with highly processed macronuclear genomes. Our analyses demonstrate that the dual nature of ciliate genomes-the presence of a "germline" micronucleus and a "somatic" macronucleus within each cell-allowed the dramatic variation in ciliate histone genes by altering functional constraints or enabling adaptive evolution of the histone H4 protein, or both.
纤毛虫谱系内部和之间不同的组蛋白H4氨基酸序列的积累，挑战了这种重要的真核生物蛋白质进化的传统观点。我们分析了13种纤毛虫的组蛋白H4序列，并将这些数据与来自充分采样的真核生物进化枝的序列进行了比较。纤毛虫的组蛋白H4在多达46%的氨基酸上彼此不同，这与该蛋白质在大多数其他真核生物中的高度保守特征形成对比。同样引人注目的是，我们在纤毛虫基因组中发现了组蛋白H4的旁系同源物，它们的氨基酸差异高达25%，而其他真核生物中的旁系同源物具有相同或几乎相同的氨基酸序列。此外，在具有高度加工的大核基因组的谱系中发现了纤毛虫中差异最大的H4蛋白。我们的分析表明，纤毛虫基因组的双重性质——每个细胞中存在一个“种系”小核和一个“体细胞”大核——通过改变功能限制或使组蛋白H4蛋白进行适应性进化，或两者兼而有之，使得纤毛虫组蛋白基因发生了显著变化。
