IDENTIFICATION OF FOSSIL SEQUENCES COMPARING SEQUENCES FROM DISTANT ORGANISMS

进化距离远的同源蛋白质的序列比对 生物体被用来精确定位结构和功能区域， 重要性在很长一段时间内，只有最受约束的部分才能保持 彼此之间的相似性。这一概念被扩展到 整个数据库，通过执行交叉比较的全面套 来自不同界和门的序列与进化距离 从真核生物/真细菌分化的20亿年到 5.5亿年的体腔辐射。显著的相似性 因此，这些集合之间对应于强烈保守的祖先 功能.使用一系列匹配/正交化过程，500 在当代序列中检测到独立的祖先类型。 这组化石只占原始数据库的4%， 与整体的40%显著匹配。因此，它实现了10倍 富集最大结构/功能的序列 重要性，是定义图案的最佳来源。 这些高度保守的序列中大约有200个对应于 蛋白质的作用并不明显，需要进一步研究。 分析.理论计算表明，500个祖先类型 迄今为止所定义的化石序列构成了大部分可检测到的化石序列， 现代序列这与另一项独立研究一致 比较3个大型新数据集：来自人类和线虫的部分cDNA， 来自酵母的染色体III的ORF。 因此，已知的蛋白质可能已经 包括代表大多数祖先特征， 体腔辐射

Sequence alignments of homologue proteins from evolutionary distant organisms are used to pinpoint regions of structural and functional importance. Over long periods only the most constrained segments retain a detectable similarity with each others. This concept was extended to the whole database, by performing cross-comparisons of comprehensive sets of sequences from various kingdoms and phyla with evolutionary distances ranging from 2 billion years for the eukaryote/eubacteria divergence to 550 million years for the coelomate radiation. Significant similarities between these sets thus correspond to strongly conserved ancestral features. Using a series of matching/orthogonalization procedures, 500 independent ancestral types were detected within contemporary sequences. This fossil set only represents 4% of the original database but significantly matches 40% of the whole. Thus, it realizes a 10-fold enrichment in sequences of the greatest structural/ functional significance and is an optimal source for the definition of motifs. Approximately 200 of those highly conserved sequences correspond to proteins the role of which is not obviously central, and warrant further analysis. Theoretical computations suggest that the 500 ancestral types defined so far constitute most of the fossil sequences detectable in modern sequences. This is consistent with another independent study comparing 3 large new datasets: partial cDNAs from human and nematode and ORFs from chromosome III of yeast. Thus, known proteins might already include representative for most ancestral features antedating the coelomate radiation.