Li Yuan, Hansson Bengt, Ghatnekar Lena, Prentice Honor C
Department of Biology, Lund University, Lund, Sweden.
Hereditas. 2017 May 18;154:11. doi: 10.1186/s41065-017-0032-6. eCollection 2017.
Phosphoglucose isomerase (PGI, EC 5.3.1.9) is an essential metabolic enzyme in all eukaryotes. An earlier study of the gene, which encodes cytosolic PGI in the grass L., revealed a marked difference in the levels of nucleotide polymorphism between the 5' and 3' portions of the gene.
In the present study, we characterized the sequence polymorphism in in more detail and examined possible explanations for the non-uniform pattern of nucleotide polymorphism across the gene.
Our study confirms that the two portions of the gene show substantially different levels of DNA polymorphism and also suggests that the peptide encoded by the 3' portion of is functionally and structurally more important than that encoded by the 5' portion. Although there was some evidence of purifying selection (/ test) on the 5' portion of the gene, the signature of purifying selection was considerably stronger on the 3' portion of the gene (/ and McDonald-Kreitman tests). Several tests support the action of balancing selection within the 5' portion of the gene. Wall's and tests were significant only for the 5' portion of the gene. There were also marked peaks of nucleotide diversity, Tajima's and the / ratio at or around a codon site (within the 5' portion of the gene) that a previous study had suggested was subject to positive diversifying selection.
Our results suggest that the two portions of the gene have been subject to different selective regimes. Purifying selection appears to have been the main force contributing to the relatively low level of polymorphism within the 3' portion of the sequence. In contrast, it is possible that balancing selection has contributed to the maintenance of the polymorphism within the 5' portion of the gene.
磷酸葡萄糖异构酶（PGI，EC 5.3.1.9）是所有真核生物中一种重要的代谢酶。早期对编码禾本科植物L.中胞质PGI的基因研究表明，该基因5'和3'部分的核苷酸多态性水平存在显著差异。
在本研究中，我们更详细地对该基因的序列多态性进行了表征，并研究了整个基因核苷酸多态性模式不一致的可能原因。
我们的研究证实，该基因的两个部分显示出显著不同的DNA多态性水平，并且还表明由该基因3'部分编码的肽在功能和结构上比由5'部分编码的肽更重要。尽管有一些证据表明在基因的5'部分存在纯化选择（/检验），但纯化选择的特征在基因的3'部分更为明显（/和麦克唐纳-克里特曼检验）。多项检验支持该基因5'部分存在平衡选择作用。沃尔氏检验和检验仅对该基因的5'部分有显著意义。在一个先前研究表明受到正向多样化选择的密码子位点（在基因的5'部分内）或其附近，核苷酸多样性、 Tajima's D值和/比值也有明显峰值。
我们的结果表明，该基因的两个部分受到了不同的选择机制。纯化选择似乎是导致序列3'部分多态性水平相对较低的主要因素。相比之下，平衡选择可能有助于维持基因5'部分的多态性。
