title: Free ribosomal RNA genes in the macronucleus of Tetrahymena.
abstract: In the macronucleus of the ciliated protozoan, Tetrahymena pyriformis GL, the genes coding for 17S and 25S rRNA exist as free, extrachromosomal molecules. About 90% of the molecules are linear with a molecular weight of 12.6 x 10(6). Most of the remainder are circles of the same size, or lariats (circles with tails). A few dimers and oligomers are found. The extrachromosomal rDNA of Tetrahymena represents a kind of gene amplification that may be common among primitive eukaryotes.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000032:analysis / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D004247:DNA / Q000032:analysis*; D004261:DNA Replication; D004270:DNA, Circular / Q000032:analysis; D005111:Extrachromosomal Inheritance; D005796:Genes; D008854:Microscopy, Electron; D009691:Nucleic Acid Denaturation; D009693:Nucleic Acid Hybridization; D010761:Phosphorus Radioisotopes; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000378:metabolism; D013768:Tetrahymena / Q000032:analysis*; D014316:Tritium; D014529:Uridine / Q000378:metabolism
chemical_list: D004270:DNA, Circular; D010761:Phosphorus Radioisotopes; D012335:RNA, Ribosomal; D014316:Tritium; D004247:DNA; D014529:Uridine