title: Use of RFLPs larger than 100 kbp to map the position and  internal organization of the nucleolus organizer region on  chromosome 2 in Arabidopsis thaliana.
abstract: In Arabidopsis thaliana ribosomal RNA genes (rRNA genes or rDNA) are grouped in two nucleolus organizer regions(NORs) that together comprise approximately 6% of the genome. The map positions of the NORs relative to other genetic markers are unknown. It was found that the restriction endonuclease Hindlll cuts once in some but not all rRNA genes to yield strain-specific RFLPs of 100-700 kb that could be visualized by pulsed-field gel electrophoresis and Southern blotting. The Hindlll RFLPs of the A. thaliana strains Columbia and Landsberg segregated among recombinant inbred lines derived from a cross between these two strains. Linkage analysis placed the NOR bearing the polymorphic Hindlll sites to the top of the upper arm of chromosome 2. The name NOR2 is suggested for this locus. Hindlll-bearing rRNA genes ere interspersed with clusters of Hindlll-less genes throughout NOR2. The observed clustering is most consistent with unequal crossing-over, or nearest-neighbor gene conversion, as the mechanism(s) that spread rRNA gene variants throughout an NOR. No meiotic cross-over events yielding a 'hybrid' NOR with multiple RFLPs from both parents were observed among the 47 recombinant inbred lines examined. However,the appearance of novel Hindlll profiles in approximately 40% of the recombinant inbred lines demonstrates that fluctuations in the distribution of rRNA gene variants occur frequently and can be readily detected on pulsed-field gels.
authors.forename: G P
authors.initials: GP
authors.lastname: Copenhaver
authors.forename: J H
authors.initials: JH
authors.lastname: Doelling
authors.forename: S
authors.initials: S
authors.lastname: Gens
authors.forename: C S
authors.initials: CS
authors.lastname: Pikaard
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D002874:Chromosome Mapping; D032461:Chromosomes, Plant; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D015247:Deoxyribonuclease HindIII; D009697:Nucleolus Organizer Region / Q000235:genetics*; D012150:Polymorphism, Restriction Fragment Length
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal; D015247:Deoxyribonuclease HindIII