Nakayama Tomohiro, Asai Satoshi, Takahashi Yasuo, Maekawa Oto, Kasama Yasuji
Division of Molecular Diagnostics, Advanced Medical Research Center, Nihon University School of Medicine, Tokyo, Japan.
Int J Biomed Sci. 2007 Mar;3(1):14-9.
Overlapping genes are relatively common in DNA and RNA viruses. There are several examples in bacterial and eukaryotic genomes, but, in general, overlapping genes are quite rare in organisms other than viruses. There have been a few reports of overlapping genes in mammalian genomes. The present study identified all of the overlapping loci and overlapping exons in every chromosome of the human genome using a public database. The total number of overlapping loci on the same and opposite strands was 949 and 743, respectively. Similarly, in every chromosome, the instances in which two loci were located on the same strand was similar to the number of 2 genes observed on opposite strands, except for chromosome 5. The number of 2 exons located on the same strand was higher than that for 2 exons located on opposite strands, indicating the presence of many comprehensive-type overlaps. The mean percentage of overlapping exons on opposite strands in each chromosome was 3.3%, suggesting that parts of the nucleotide sequences of 26,501 exons are used to produce 2 transcribed products from each strand. The ratio of the number of overlapping regions to chromosomal length revealed that, on chromosomes 22, 17 and 19, ratios were high for both types of 2 loci, with exons located on the same and opposite strands. Ratios were low on chromosomes Y, 13 and 18. These results show that all overlapping types are distributed throughout the human genome, but that distributions differ for each chromosome.
重叠基因在DNA和RNA病毒中相对常见。在细菌和真核生物基因组中也有一些例子，但总体而言，除病毒外，重叠基因在其他生物体中相当罕见。关于哺乳动物基因组中的重叠基因已有一些报道。本研究利用一个公共数据库确定了人类基因组每条染色体上所有的重叠位点和重叠外显子。同一条链和相反链上重叠位点的总数分别为949个和743个。同样，在每条染色体中，除了5号染色体外，两个位点位于同一条链上的情况与位于相反链上的两个基因的数量相似。位于同一条链上的两个外显子的数量高于位于相反链上两个外显子的数量，这表明存在许多综合型重叠。每条染色体中相反链上重叠外显子的平均百分比为3.3%，这表明26,501个外显子的部分核苷酸序列被用于从每条链产生2种转录产物。重叠区域数量与染色体长度的比率显示，在22号、17号和19号染色体上，两种类型的两个位点（位于同一条链和相反链上的外显子）的比率都很高。在Y染色体、13号和18号染色体上比率较低。这些结果表明，所有重叠类型都分布在整个人类基因组中，但每条染色体的分布有所不同。
