期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：19
页码：11133-11138
DOI：10.1073/pnas.1831011100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The Arabidopsis genome project assembled 15 megabases of heterochromatic sequence, facilitating investigations of heterochromatin assembly, maintenance, and structure. In many species, large quantities of methylcytosine decorate heterochromatin; these modifications are typically maintained by methyltransferases that recognize newly replicated hemimethylated DNA. We assessed the extent and patterns of Arabidopsis heterochromatin methylation by amplifying and sequencing genomic DNA treated with bisulfite, which converts cytosine, but not methylcytosine, to uracil. This survey revealed unexpected asymmetries in methylation patterns, with one helix strand often exhibiting higher levels of methylation. We confirmed these observations both by immunoprecipitating methylated DNA strands and by restriction enzyme digestion of amplified, bisulfite-treated DNA. We also developed a primer-extension assay that can monitor the methylation status of an entire chromosome, demonstrating that strand-specific methylation occurs predominantly in the centromeric regions. Conventional models for methylation maintenance do not explain these unusual patterns; instead, new models that allow for strand specificity are required. The abundance of Arabidopsis strand-specific modifications points to their importance, perhaps as epigenetic signals that mark the heterochromatic regions that confer centromere activity.
关键词：heterochromatin ; centromere ; methylcytosine ; DNA methylation
