title: Evidence for methylation of inactive human rRNA genes in amplified regions.
abstract: In two unrelated families, the short arm of a 14p+ marker chromosome contains an increased number of copies of the 18S + 28S rRNA genes without a comparable increase in the transcriptional activity, as shown by silver staining. The DNA in this region is highly enriched in 5-methylcytosine, as shown by specific antibody binding. In contrast, the owl monkey and cat have a single major nucleolus organizer region (NOR) per haploid genome; these NORs contain about the same number of rRNA genes as the 14p+ chromosome but are not methylated. These findings suggest that most of the amplified human rRNA genes on the 14p+ chromosomes have been inactivated by a process involving DNA methylation.
mesh_terms: D000818:Animals; D001029:Aotus trivirgatus / Q000235:genetics; D002415:Cats; D002478:Cells, Cultured; D002871:Chromosome Banding; D002874:Chromosome Mapping; D002901:Chromosomes, Human, 13-15; D004261:DNA Replication; D005260:Female; D005796:Genes; D005819:Genetic Markers; D006801:Humans; D008214:Lymphocytes / Q000648:ultrastructure; D008297:Male; D012335:RNA, Ribosomal / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D005819:Genetic Markers; D012335:RNA, Ribosomal