Fukuda Y, Washio T, Tomita M
Laboratory for Bioinformatics, Department of Environmental Information and Graduate School of Media and Governance, Keio University, 5322 Endo, Fujisawa 252, Japan.
Nucleic Acids Res. 1999 Apr 15;27(8):1847-53. doi: 10.1093/nar/27.8.1847.
Overlapping genes are defined, in this paper, as a pair of adjacent genes whose coding regions are partly overlapping. We systematically analyzed all overlapping genes in the genomes of two closely related species: Mycoplasma genitalium and Mycoplasma pneumoniae. Careful comparisons were made for homologous genes that are overlapped in one species but not in the other. This comparative analysis allows us to propose a model of how overlapping genes emerged in the course of evolution. It was found that overlapping genes were generated primarily due to the loss of a stop codon in either gene, in many cases, the absence of which resulted in elongation of the 3' end of the gene's coding region. More specifically, the loss of the stop codon took place as a result of the following events: deletion of the stop codon (64.4%), point mutation at the stop codon (4.4%), and frame shift at the end of the coding region (6.7%). Overlapping genes, in a sense, can be thought of as the results of evolutionary pressure to minimize genome size. However, our analysis indicates that many overlapping genes, at least in the genomes of M.genitalium and M.pneumoniae, are due to incidental elongation of the coding regions.
在本文中，重叠基因被定义为一对相邻基因，其编码区域部分重叠。我们系统地分析了两个密切相关物种基因组中的所有重叠基因：生殖支原体和肺炎支原体。对于在一个物种中重叠而在另一个物种中不重叠的同源基因进行了仔细比较。这种比较分析使我们能够提出一个关于重叠基因在进化过程中如何出现的模型。研究发现，重叠基因主要是由于两个基因中任一基因的终止密码子缺失而产生的，在许多情况下，终止密码子的缺失导致基因编码区域3'端的延伸。更具体地说，终止密码子的缺失是由以下事件导致的：终止密码子的缺失（64.4%）、终止密码子处的点突变（4.4%）以及编码区域末端的移码（6.7%）。从某种意义上说，重叠基因可以被认为是基因组大小最小化进化压力的结果。然而，我们的分析表明，许多重叠基因，至少在生殖支原体和肺炎支原体的基因组中，是由于编码区域的偶然延伸。
