title: Nuclear rDNA in Euglena gracilis: paucity of chromosomal units and replication of extrachromosomal units.
abstract: Copy number of chromosomal rDNA units was investigated in two Euglena gracilis wild-type strains. It was established by dot blot analysis that these strains possess about four integrated units per haploid genome. This is the first example of a photosynthetic cell with only a few chromosomal ribosomal genes. In addition to these units, Euglena has 800 to 4000 extrachromosomal rDNA units. Electron microscopy revealed that these free rDNA circles bear a replication origin, and intermediates of replication show a D-loop structure.
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000032:analysis; D004261:DNA Replication; D004270:DNA, Circular / Q000648:ultrastructure; D004275:DNA, Ribosomal / Q000235:genetics* / Q000648:ultrastructure; D005056:Euglena gracilis / Q000235:genetics* / Q000648:ultrastructure; D005111:Extrachromosomal Inheritance; D012091:Repetitive Sequences, Nucleic Acid; D012093:Replicon
chemical_list: D004270:DNA, Circular; D004275:DNA, Ribosomal