EVIDENCE THAT MOST HUMAN ALU SEQUENCES WERE INSERTED IN A PROCESS THAT CEASED ABOUT 30 MILLION YEARS AGO
EVIDENCE THAT MOST HUMAN ALU SEQUENCES WERE INSERTED IN A PROCESS THAT CEASED ABOUT 30 MILLION YEARS AGO
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DOI：
10.1073/pnas.91.13.6148
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发表时间：
1994-06-21
影响因子：
11.1
通讯作者：
BRITTEN, RJ
中科院分区：
文献类型：
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作者：
BRITTEN, RJ
灵长类Alu散布的重复序列可以根据一组诊断位置上的共同核苷酸被细分为几类。每一类Alu序列显然都是过去高度保守的类特异性源基因的转录本逆转录转座的结果，这些基因在诊断位置上彼此不同，大多数位置上的核苷酸在源基因中是相同的，因此在插入时在所有Alu序列中是相同的。这些CONSBI(插入前保守)位置是有用的，因为插入后发生的变化是可识别的，并且核苷酸替换、插入和缺失导致的差异是有用的。在CONSBI位置的Alu序列的离散度是自插入类以来的时间的度量。大多数ALU序列属于一类(被鉴定为II类)，并且它特别适合于这种检查，因为几乎全长序列现已为这类中的近1000个成员所知。第二类成员的平均分化表明，该类的平均年龄约为4000万年。II类散度分布精确地符合两个泊松分布之和。这意味着II类Alu序列是从两次大规模的插入许多Alu序列的过去事件中派生出来的。在这个模型中，较年轻的II类序列子集(对应于基因组中约300,000个拷贝)在CONSBI位置上的平均分歧为5%。较老的一组II类序列(对应于大约150,000个基因组拷贝)具有9%的平均分歧。根据灵长类DNA序列的漂移率，插入事件可能发生在3000-5000万年前。泊松分布的良好拟合度表明，自3000万年前以来，没有显著数量的II类成员被插入。
The primate Alu interspersed repeats can be subdivided into classes on the basis of shared nucleotides at a set of diagnostic positions. Each of the classes of Alu sequences is apparently the result of past retrotransposition of transcripts of highly conserved class-specific source genes that differed from each other at the diagnostic positions, The nucleotides at the majority of positions are identical among the source genes and therefore were identical among all of the Alu sequences at the time of their insertion. These CONSBI (conserved before insertion) positions are useful because the changes that have occurred after insertion are recognizable and the divergence resulting from nucleotide substitutions, insertions, and deletions is informative. The divergence of Alu sequences at the CONSBI positions is a measure of the time since a class was inserted. The greatest majority of Alu sequences are in one class (identified as class II), and it is particularly suitable for such examination, since nearly full-length sequences are now known for nearly a thousand members of this class. The average divergence of class II members indicates that the class has an average age of about 40 million years. The distribution in divergence of class II accurately fits a sum of two Poisson distributions. The implication is that class II Alu sequences were derived from two massive past events of insertion of many Alu sequences. In this model the younger subset of class II sequences (corresponding to about 300,000 copies in the genome) has an average divergence of 5% at CONSBI positions. The older set of class II sequences (corresponding to about 150,000 genomic copies) has a 9% average divergence. Based on the drift rate of primate DNA sequences, the events of insertion probably occurred 30-50 million years ago. The goodness of the fit to the Poisson distribution indicates that no significant number of members of class II have been inserted since 30 million years ago.