IDENTIFICATION OF FOSSIL SEQUENCES COMPARING SEQUENCES FROM DISTANT ORGANISMS

进化距离的同源蛋白的序列比对 生物体被用来精确定位结构和功能区域 重要性。在较长时间内，仅保留最受约束的线段 彼此之间可察觉到的相似性。这一概念被扩展到 整个数据库，通过执行全面的交叉比较 来自不同王国和门类的序列集，具有进化 真核生物/真细菌的距离从20亿年不等 体腔辐射的发散度为5.5亿年。 因此，这些集合之间的显著相似性对应于 高度保守的祖先特征。使用一系列 匹配/正交化程序，500种独立祖先类型 在同时代的序列中被检测到。这块化石只有 代表原始数据库的4%，但与40%非常匹配 在整个世界里。因此，它在序列中实现了10倍的丰富 具有最大的结构/功能意义，是最理想的 主题定义的来源。其中大约200个高度 保守的序列对应于蛋白质，而蛋白质的作用不是 显然是核心问题，需要进一步分析。理论上的 计算表明，到目前为止定义的500种祖先类型 构成了在现代层序中可检测到的大多数化石序列。 这与另一项独立研究一致，该研究比较了3个大型新的 数据集：来自人类和线虫的部分cDNA和来自 酵母的第三号染色体。因此，已知的蛋白质可能已经包括 代表大多数先于体腔动物的祖先特征 辐射。一个包含550个古代序列原型的数据库已经被 通过计算机网络建立并提供给社区。

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 other. 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. A database of 550 ancient sequence prototypes has been constituted and made available to the community by computer network.