Okamura Kohji, Nakai Kenta
Human Genome Centre, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Mol Biol Evol. 2008 Jun;25(6):1231-8. doi: 10.1093/molbev/msn071. Epub 2008 Mar 25.
The fact that promoters are essential for the function of all genes presents the basis of the general idea that retrotranspositions give rise to processed pseudogenes. However, recent studies have demonstrated that some retrotransposed genes are transcriptionally active. Because promoters are not thought to be retrotransposed along with exonic sequences, these transcriptionally active genes must have acquired a functional promoter by mechanisms that are yet to be determined. Hence, comparison between a retrotransposed gene and its source gene appears to provide a unique opportunity to investigate the promoter creation for a new gene. Here, we identified 29 gene pairs in the human genome, consisting of a functional retrotransposed gene and its parental gene, and compared their respective promoters. In more than half of these cases, we unexpectedly found that a large part of the core promoter had been transcribed, reverse transcribed, and then integrated to be operative at the transposed locus. This observation can be ascribed to the recent discovery that transcription start sites tend to be interspersed rather than situated at 1 specific site. This propensity could confer retrotransposability to promoters per se. Accordingly, the retrotransposability can explain the genesis of some alternative promoters.
启动子对于所有基因的功能至关重要，这一事实构成了反转录转座产生加工假基因这一普遍观点的基础。然而，最近的研究表明，一些反转录转座基因具有转录活性。由于启动子不被认为会与外显子序列一起反转录转座，这些具有转录活性的基因必定是通过尚未确定的机制获得了功能性启动子。因此，比较一个反转录转座基因与其源基因似乎为研究新基因的启动子产生提供了一个独特的机会。在这里，我们在人类基因组中鉴定出29对基因，由一个功能性反转录转座基因及其亲本基因组成，并比较了它们各自的启动子。在超过半数的这些案例中，我们意外地发现，核心启动子的很大一部分已被转录、反转录，然后整合到转座位点发挥作用。这一观察结果可归因于最近的发现，即转录起始位点往往是散布的，而不是位于1个特定位点。这种倾向可能赋予启动子本身反转录转座能力。相应地，反转录转座能力可以解释一些替代启动子的起源。
