Hamdi H, Nishio H, Zielinski R, Dugaiczyk A
Department of Biochemistry, University of California, Riverside, CA, 92521, USA.
J Mol Biol. 1999 Jun 18;289(4):861-71. doi: 10.1006/jmbi.1999.2797.
Over the past 60 million years, or so, approximately one million copies of Alu DNA repeats have accumulated in the genome of primates, in what appears to be an ongoing process. We determined the phylogenetic distribution of specific Alu (and other) DNA repeats in the genome of several primates: human, chimpanzee, gorilla, orangutan, baboon, rhesus, and macaque. At the population level studied, the majority of the repeats was found to be fixed in the primate species. Our data suggest that new Alu elements arise in unique, irreversible events, in a mechanism that seems to preclude precise excision and loss. The same insertions did not arise independently in two species. Once inserted and genetically fixed, the DNA elements are retained in all descendant lineages. The irreversible expansion of Alu s introduces a vector of time into the evolutionary process, and provides realistic (rather than statistical) answers to questions on phylogenies. In contrast to point mutations, the present distribution of individual Alu s is congruent with just one phylogeny. We submit that only irreversible and taxonomically relevant events are at the molecular basis of evolution. Most point mutations do not belong to this category.
在过去约6000万年的时间里，灵长类动物基因组中积累了大约100万个Alu DNA重复序列拷贝，这似乎是一个仍在进行的过程。我们确定了几种灵长类动物（人类、黑猩猩、大猩猩、猩猩、狒狒、恒河猴和猕猴）基因组中特定Alu（及其他）DNA重复序列的系统发育分布。在所研究的种群水平上，发现大多数重复序列在灵长类物种中是固定的。我们的数据表明，新的Alu元件产生于独特的、不可逆转的事件中，其机制似乎排除了精确切除和丢失的可能性。相同的插入在两个物种中不会独立出现。一旦插入并在基因上固定下来，这些DNA元件就会保留在所有后代谱系中。Alu序列的不可逆扩增将时间向量引入了进化过程，并为有关系统发育的问题提供了现实的（而非统计的）答案。与点突变不同，单个Alu序列的当前分布仅与一种系统发育一致。我们认为，只有不可逆转且与分类学相关的事件才是进化的分子基础。大多数点突变不属于这一类别。
