Meyer P, Niedenhof I, ten Lohuis M
Max-Delbrück-Laboratorium in der MPG, Cologne, Germany.
EMBO J. 1994 May 1;13(9):2084-8. doi: 10.1002/j.1460-2075.1994.tb06483.x.
A considerable proportion of cytosine residues in plants are methylated at carbon 5. According to a well-accepted rule, cytosine methylation is confined to symmetrical sequences such as CpG and CpNpG, which provide the signal for faithful transmission of symmetrical methylation patterns by maintenance methylase. Using a genomic sequencing technique, we have analysed cytosine methylation patterns within a hypermethylated and a hypomethylated state of a transgene in Petunia hybrida. Examination of a part of the transgene promoter revealed that in both states m5C residues located within non-symmetrical sequences could be detected. Non-symmetrical C residues in the two states were methylated at frequencies of 5.9 and 31.9%, respectively. Methylation appeared to be distributed heterogeneously, but some DNA regions were more intensively methylated than others. Our results show that at least in a transgene, a heterogeneous methylation pattern, which does not depend on symmetry of target sequences, can be established and conserved.
植物中相当一部分胞嘧啶残基在5位碳上发生甲基化。根据一个广泛接受的规则，胞嘧啶甲基化局限于对称序列，如CpG和CpNpG，这些序列为维持甲基化酶忠实地传递对称甲基化模式提供信号。我们使用基因组测序技术，分析了矮牵牛中转基因的高甲基化和低甲基化状态下的胞嘧啶甲基化模式。对转基因启动子的一部分进行检测发现，在这两种状态下都能检测到位于非对称序列内的5-甲基胞嘧啶（m5C）残基。两种状态下非对称C残基的甲基化频率分别为5.9%和31.9%。甲基化似乎呈不均匀分布，但一些DNA区域的甲基化程度比其他区域更高。我们的结果表明，至少在转基因中，可以建立并维持一种不依赖于靶序列对称性的不均匀甲基化模式。
