MBE Advance Access originally published online on March 25, 2008
Molecular Biology and Evolution 2008 25(6):1231-1238; doi:10.1093/molbev/msn071
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Research Articles |
Retrotransposition as a Source of New Promoters
Human Genome Centre, Institute of Medical Science, University of Tokyo, Tokyo, Japan; and Institute for Bioinformatics Research and Development (BIRD), Japan Science and Technology Agency (JST), Kawaguchi, Japan
E-mail: knakai{at}ims.u-tokyo.ac.jp
Accepted for publication March 18, 2008.
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.
Key Words: promoter transcription start site retrotransposition alternative promoter human genome molecular evolution
Takashi Gojobori, Associate Editor