POSITIONED NUCLEOSOMES INHIBIT DAM METHYLATION IN-VIVO
POSITIONED NUCLEOSOMES INHIBIT DAM METHYLATION IN-VIVO
复制标题
DOI：
10.1073/pnas.91.4.1361
复制
发表时间：
1994-02-15
影响因子：
11.1
通讯作者：
SIMPSON, RT
中科院分区：
文献类型：
--
作者：
KLADDE, MP;SIMPSON, RT
大肠杆菌Dam DNA甲基转移酶在酿酒酵母中表达时可以甲基化基因组中的GATC位点。其他人观察到特定位点甲基化水平的变化，并认为这些变化与转录状态或染色体背景有关。为了直接测试核小体位置对Dam甲基转移酶修饰染色质上GATC位点的能力的影响，我们分析了表达Dam的酵母菌株中含有精确定位核小体的小染色体。通过寡核苷酸探测程序严格定量了各个GATC位点的甲基化水平。在连接体和相邻的核小体相关DNA的21 bp内，GATC位点高度甲基化，而组蛋白-DNA靠近核小体假二联体的接触则严重抑制甲基化。其他dna -蛋白质复合物也会干扰Dam甲基化。这些数据与核小体通过限制反式作用因子进入DNA对DNA生物学功能施加抑制影响的模型一致。
Escherichia coli Dam DNA methyltransferase can methylate genomic GATC sites when expressed in Saccharomyces cerevisiae. Others have observed changes in the level of methylation at specific sites and suggested that these changes are related to transcriptional state or chromosomal context. To test directly the influence of nucleosome location on the ability of Dam methyltransferase to modify GATC sites in chromatin, we analyzed minichromosomes containing precisely positioned nucleosomes in dam-expressing yeast strains. Levels of methylation at individual GATC sites were rigorously quantified by an oligonucleotide-probing procedure. Within the linker and adjacent 21 bp of nucleosome-associated DNA, GATC sites were highly methylated, whereas methylation was severely inhibited by histone-DNA contacts nearer to the nucleosomal pseudodyad. Other DNA-protein complexes also interfere with Dam methylation. These data are consistent with a model in which nucleosomes exert a repressive influence on the biological functions of DNA by restricting access of trans-acting factors to DNA.