Fulnecek J, Matyásek R, Kovarík A, Bezdek M
Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno.
Mol Gen Genet. 1998 Aug;259(2):133-41. doi: 10.1007/s004380050798.
Genomic sequencing was used to localise 5-methylcytosine residues in individual DNA strands of 5S rRNA genes in tobacco. The density of methylation along the sequence was high in both strands, exceeding the average methylation density of the tobacco genome. Besides methylation of CG and CNG sequences, considerable amounts of mC were found in non-symmetrical sites. Among 69 sequenced clones obtained from leaf DNA we did not detect any non-methylated clone, and Southern blot hybridisation analysis also failed to suggest the presence of methylation-free 5S rDNA units in the tobacco genome. Differences were observed among methylation patterns of individual sequenced clones. This heterogeneity reflects either heterogeneity among individual members of 5S rRNA gene cluster or differences among individual cells. Methylation of CNG and non-symmetrical sites can be efficiently reduced by treatment with dihydroxypropyladenine, an inhibitor of S-adenosylhomocysteine hydrolase.
利用基因组测序技术对烟草5S rRNA基因单链DNA中的5-甲基胞嘧啶残基进行定位。两条链上沿序列的甲基化密度都很高，超过了烟草基因组的平均甲基化密度。除了CG和CNG序列的甲基化外，在非对称位点还发现了大量的5-甲基胞嘧啶（mC）。从叶片DNA获得的69个测序克隆中，我们未检测到任何未甲基化的克隆，Southern杂交分析也未表明烟草基因组中存在无甲基化的5S rDNA单元。在各个测序克隆的甲基化模式之间观察到差异。这种异质性反映了5S rRNA基因簇单个成员之间的异质性或单个细胞之间的差异。用S-腺苷同型半胱氨酸水解酶抑制剂二羟丙基腺嘌呤处理可有效降低CNG和非对称位点的甲基化。
