MRC Clinical and Population Cytogenetics Unit, Western General Hospital, Crewe Road, Edinburgh EH4 2XU, UK.
EMBO J. 1988 Aug;7(8):2295-9. doi: 10.1002/j.1460-2075.1988.tb03072.x.
The genomes of many higher plant species are the most highly methylated among eukaryotes. We report here that in spite of their heavy methylation, genomic DNAs from four plant species contain a fraction that is very rich in non-methylated sites. The fraction was characterized in maize where it represents about 2.5% of the total nuclear genome. In order to establish the genomic origin of the fraction, three maize genes containing clustered CpG were tested for methylation and were found to be non-methylated in the CpG-rich regions. By contrast, tested CpGs were methylated in a gene whose sequence showed no clustering of CpG. These observations suggest that the CpG-rich fraction of plants is at least partially derived from non-methylated regions that are associated with genes. A similar phenomenon has been described in vertebrate genomes. We discuss the evolution of CpG islands in both groups of organisms, and their possible uses in mapping and gene isolation in plants.
许多高等植物物种的基因组在真核生物中是甲基化程度最高的。我们在这里报告,尽管它们高度甲基化,但来自四个植物物种的基因组 DNA 含有一部分富含非甲基化位点。该部分在玉米中进行了表征,在玉米中,它约占总核基因组的 2.5%。为了确定该部分的基因组起源,对三个含有簇状 CpG 的玉米基因进行了甲基化测试,结果发现 CpG 丰富区域的基因未甲基化。相比之下,在一个序列中没有 CpG 聚类的基因中,测试的 CpG 被甲基化。这些观察结果表明,植物的 CpG 丰富部分至少部分来源于与基因相关的非甲基化区域。脊椎动物基因组中也描述了类似的现象。我们讨论了这两组生物中 CpG 岛的进化及其在植物中基因定位和分离中的可能用途。