title: Tandem repeats in extrachromosomal ribosomal DNA of Dictyostelium discoideum, resulting from chromosomal mutations.
abstract: Extrachromosomal ribosomal DNA in the simple eukaryote Dictyostelium discoideum is readily separated from chromosomal DNA by orthogonal field electrophoresis (OFAGE), forming a prominent band in the 110-kb region of the gel. Here we show that mutations in at least two chromosomal genes give rise to a ladder of rDNA bands increasing in size up to about 300 kb. One of these mutations, the rrcA350 allele, which is recessive to wild type and maps to the centromere-proximal region of linkage group II, has an unstable phenotype; spontaneous revertants, which no longer exhibit the rDNA ladder, have been recovered. Another mutation rrc-351, provisionally mapped to linkage group IV, is dominant to wild type. The rDNA ladder is caused by concatamerization of a 34-kb fragment in the nontranscribed central spacer region of the 88-kb linear rDNA palindrome. Restriction enzyme analysis has revealed that each concatamer is generated by crossovers between two rDNA molecules.
authors.affiliation: School of Biological Sciences, Macquarie University, Sydney, New South Wales, Australia.
authors.forename: R A
authors.initials: RA
authors.lastname: Cole
authors.forename: K L
authors.initials: KL
authors.lastname: Williams
mesh_terms: D000818:Animals; D004271:DNA, Fungal / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D015246:Deoxyribonuclease EcoRI; D004023:Dictyostelium / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods; D005111:Extrachromosomal Inheritance / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D015246:Deoxyribonuclease EcoRI