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：1981
卷号：78
期号：1
页码：489-493
DOI：10.1073/pnas.78.1.489
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：In a rat hepatoma cell line, H4-IIE-C3, a 10-fold excess of 18S and 28S rRNA genes has been found in amplified chromosome regions. Antibodies to 5-methylcytidine bound extensively to the DNA of these regions, indicating a high level of DNA methylation. Most of the amplified rRNA genes were transcriptionally inactive, as shown by their failure to stain with silver. DNAs from the tumor cells and control rat hepatocytes grown with L-[methyl-14C]methionine were digested with restriction endonuclease EcoRI; the DNA fragments were separated by agarose gel electrophoresis, denatured, transferred to nitrocellulose filters, and hybridized to 32P-labeled rRNA or cDNA. Fragments containing the 18S or 28S rRNA coding sequences occurred in three major size classes; all three were rich in 5-methylcytosine. Analysis of EcoRI fragments of DNA from the tumor and control cells after digestion with Hpa II or Msp I endonuclease indicated that the 5'-C-C-G-G-3' sequences in most of the amplified rRNA genes were methylated. Analysis of the fragments produced by digestion with Hha I endonuclease indicated a high degree of methylation within its recognition sequence in the amplified rRNA genes as well. The association of hypermethylation with restricted transcriptional activity suggests that DNA methylation may regulate the activity of the rRNA genes.
