Comprehensive analysis of CpG islands in human chromosomes 21 and 22
Comprehensive analysis of CpG islands in human chromosomes 21 and 22
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DOI：
10.1073/pnas.052410099
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发表时间：
2002-03-19
影响因子：
11.1
通讯作者：
Jones, PA
中科院分区：
文献类型：
--
作者：
Takai, D;Jones, PA
CpG岛是基因组中含有5-甲基胞嘧啶的生物体中基因的有用标记。此外，位于基因启动子区的CpG岛在X染色体失活、印记和基因组内寄生虫沉默等过程中可在基因沉默中发挥重要作用。什么构成CpG岛的普遍接受的定义由Gardiner-Garden和Frommer在1987年提出[Gardiner-Garden，M. & Frommer，M.等人（1987）J. Mol. 196，261-282]作为具有50%的C+G含量和超过0.6的观察到的CpG/预期的CpG的200-bp DNA片段。任何关于CpG岛的定义都有些武断，而这个定义是在哺乳动物基因组测序之前得出的，它将包括许多不一定与基因控制区域相关，但与基因组内寄生虫相关的序列。因此，我们使用了完整的人类21号和22号染色体的基因组序列，通过使用我们开发的搜索算法来检查不同序列类别中CpG岛的特性。大于500的DNA区域，G+C等于或大于55%，观察到CpG;预期CpG为0.65，更可能与基因的5'区域相关，该定义排除了大多数重复元件。我们还使用基因组序列来显示人类基因组中的强CpG抑制和黑腹果蝇和酿酒酵母中的轻微抑制。这一发现与最近在果蝇中检测到的5-甲基胞嘧啶一致，并可能表明S。酿酒酵母已经或曾经有过CpG甲基化。
CpG islands are useful markers for genes in organisms containing 5-methylcytosine in their genomes. In addition, CpG islands located in the promoter regions of genes can play important roles in gene silencing during processes such as X-chromosome inactivation, imprinting, and silencing of intragenomic parasites. The generally accepted definition of what constitutes a CpG island was proposed in 1987 by Gardiner-Garden and Frommer [Gardiner-Garden, M. & Frommer, M. (1987) J. Mol. Biol. 196, 261-282] as being a 200-bp stretch of DNA with a C+G content of 50% and an observed CpG/expected CpG in excess of 0.6. Any definition of a CpG island is somewhat arbitrary, and this one, which was derived before the sequencing of mammalian genomes, will include many sequences that are not necessarily associated with controlling regions of genes but rather are associated with intragenomic parasites. We have therefore used the complete genomic sequences of human chromosomes 21 and 22 to examine the properties of CpG islands in different sequence classes by using a search algorithm that we have developed. Regions of DNA of greater than 500 by with a G+C equal to or greater than 55% and observed CpG; expected CpG of 0.65 were more likely to be associated with the 5' regions of genes and this definition excluded most Alu-repetitive elements. We also used genome sequences to show strong CpG suppression in the human genome and slight suppression in Drosophila melanogaster and Saccharomyces cerevisiae. This finding is compatible with the recent detection of 5-methylcytosine in Drosophila, and might suggest that S. cerevisiae has, or once had, CpG methylation.