title: The flax ribosomal RNA-encoding genes are arranged in tandem at a single locus interspersed by 'non-rDNA' sequences.
abstract: The ribosomal RNA (rRNA)-encoding genes (rDNA) in flax, estimated to be present in about 2400 copies per diploid nucleus, have been reported as a single homogeneous repeat unit of 8.6 kb. In situ hybridization analysis indicated that these genes were located at a single site on one pair of chromosomes. However, an analysis of a flax variety, CI 1303, has revealed heterogeneity in the intergenic spacer of the rDNA repeat unit. A genetic analysis of rDNA inheritance in two flax lines, Stormont Cirrus and CI 1303, has again supported the observation that there is a single rDNA locus in this plant species. Screening of four different genomic libraries made in methylation-sensitive and -insensitive systems, and the analysis of 40 phage clones, demonstrate a much higher number than that expected of junctions between rDNA and non-rDNA. Direct evidence of rRNA-encoding genes being present in tandem comes from a few phage clones that contain more than two rDNA repeats. The evidence presented here indicates that rDNA, although present at a single locus in tandem arrays, may be interrupted frequently by other non-rDNA sequences, thus giving rise to questions about their organization into long tandem arrays.
authors.affiliation: Department of Biology, Case Western Reserve University, Cleveland, OH 44106.
authors.forename: M L
authors.initials: ML
authors.lastname: Agarwal
authors.forename: J
authors.initials: J
authors.lastname: Aldrich
authors.forename: A
authors.initials: A
authors.lastname: Agarwal
authors.forename: C A
authors.initials: CA
authors.lastname: Cullis
mesh_terms: D015139:Blotting, Southern; D002874:Chromosome Mapping; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004275:DNA, Ribosomal / Q000235:genetics* / Q000302:isolation & purification; D017343:Genes, Plant; D010944:Plants / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics*; D015183:Restriction Mapping
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; D004247:DNA