Eukaryogenesis, the origin of the eukaryotes, is still poorly understood. Herein, we show how a detailed all-kingdom phylogenetic analysis overlaid with a map of key biochemical features can provide valuable clues. The photolyase/cryptochrome family of proteins are well known to repair DNA in response to potentially harmful effects of sunlight and to entrain circadian rhythms. Phylogenetic analysis of photolyase/cryptochrome protein sequences from a wide range of prokaryotes and eukaryotes points to a number of horizontal gene transfer events between ancestral bacteria and ancestral eukaryotes. Previous experimental research has characterised patterns of tryptophan residues in these proteins that are important for photoreception, specifically a tryptophan dyad, a canonical tryptophan triad, an alternative tryptophan triad, a tryptophan tetrad and an alternative tetrad. Our results suggest that the spread of the different triad and tetrad motifs across the kingdoms of life accompanied the putative horizontal gene transfers and is consistent with multiple bacterial contributions to eukaryogenesis.

真核生物的起源真核发生仍然知之甚少。在此，我们展示了覆盖关键生化特征图的详细全界系统发育分析如何提供有价值的线索。众所周知，光解酶/隐色素家族的蛋白质可以修复 DNA，以应对阳光的潜在有害影响并调节昼夜节律。来自各种原核生物和真核生物的光解酶/隐色素蛋白序列的系统发育分析指出了祖先细菌和祖先真核生物之间的许多水平基因转移事件。先前的实验研究已经表征了这些蛋白质中对光接收很重要的色氨酸残基模式，特别是色氨酸二元组、经典色氨酸三元组、替代色氨酸三元组、色氨酸四分体和替代四分体。我们的结果表明，不同的三联体和四联体基序在生命王国中的传播伴随着假定的水平基因转移，并且与多种细菌对真核发生的贡献一致。