title: Methylation of mouse ribosomal RNA genes.
abstract: Ribosomal DNA (rDNA) methylation was studied in various strains of mice. We used restriction enzymes that are sensitive to methylation and a cloned probe containing the transcribed spacer and part of the 18S and 28S gene. Strains C3H/He3, C57/B6-3, and AKR/J were found to have less than 9% of the rDNA methylated. In sharp contrast, Balb/c mice showed 30-50% of the Hpa II and Hha I sites to be methylated. Further study of the Balb/c DNA showed that there are three groups of rDNA sequences. In the first group, all the Hpa II and Hha I sites are almost completely unmethylated; in the second group these sites are all methylated (greater than 30 sites for each enzyme); in the third group most sites are methylated, but there are discrete hypomethylation sites. These hypomethylation positions are at similar sites for both Hpa II and Hha I and show a tissue-specific pattern. Comparison of AKR/J with Balb/c copy level showed that AKR/J had about 60% fewer rDNA genes. The rDNA methylation level might thus be correlated directly with the number of rDNA genes. Finally, analysis of F1 mice from a cross between Balb/c and AKR/J showed both low copy number and low methylation levels.
mesh_terms: D000818:Animals; D004247:DNA / Q000235:genetics*; D004262:DNA Restriction Enzymes; D004275:DNA, Ribosomal; D005784:Gene Amplification; D008297:Male; D008745:Methylation; D051379:Mice; D008815:Mice, Inbred Strains; D009693:Nucleic Acid Hybridization; D012335:RNA, Ribosomal / Q000235:genetics*; D013045:Species Specificity
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; D004247:DNA; D004262:DNA Restriction Enzymes