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哺乳动物基因组DNA中5-mC约占胞嘧啶总量的2% 7%,绝大多数5-mC存在于CpG二联核苷(CpG doublets)。 结构基因5′端附近富含CpG二联核苷的区域称为 cpG岛( CpG islands) DNA甲基化
结构基因5’端附近富含CpG二联核苷的区域称为 CpG岛(CpG islands)。 DNA甲基化 哺乳动物基因组DNA中5-mC约占胞嘧啶总量的2%-- 7%，绝大多数5-mC存在于CpG二联核苷(CpG doublets)
CH, CH, CH CH,CH, CH DNA CH, CH C CH, CH, CH CH, CH3 CH3 ACCCGTCAGATGCGATG TGGGCAGTCTACGCTAC CH CH Fig. (A) The human genome is decorated with methyl groups, which occur nearly exclusively at cytosine residues within the symmetric CpG dinucleotide
基因调控元件(如启动子)所含CpG岛中的 5-mC会阻碍转录因子复合体与DNA的结合 所以DNA甲基化一般与基因沉默(gene silence)相关联;而非基化(non methylated)_般与基因的活化(gene activation)相关联。而去甲基化 ( demethylation往往与一个沉默基因的重 新激活( reactivation相关联。 DNA甲基化
基因调控元件(如启动子)所含CpG岛中的 5-mC会阻碍转录因子复合体与DNA的结合 ，所以DNA甲基化一般与基因沉默(gene silence)相关联； 而非甲基化(nonmethylated)一般与基因的活化(gene activation)相关联。而去甲基化 (demethylation)往往与一个沉默基因的重 新激活(reactivation)相关联。 DNA甲基化
A CpG island Promoter Exon 1 Exon 2 Transcription Promoter Exon 1 EXon 2 Fig. Unmethylated cytosines are found at high densities in CpG islands, which usually map to the promoter and first exon regions of housekeeping genes. (A) The fully unmethylated state of a promoter CpG island (open lollipops) is associated with transcriptional activity whereas(B)dense methylation(closed lollipops)causes transcriptional silencing