title: Expansion and contraction of ribosomal DNA repeats in Saccharomyces cerevisiae: requirement of replication fork blocking (Fob1) protein and the role of RNA polymerase I.
abstract: Saccharomyces cerevisiae carries approximately 150 copies of rDNA in tandem repeats. It was found that the absence of an essential subunit of RNA polymerase I (Pol I) in rpa135 deletion mutants triggers a gradual decrease in rDNA repeat number to about one-half the normal level. Reintroduction of the missing RPA135 gene induced a gradual increase in repeat number back to the normal level. Gene FOB1 was shown to be essential for both the decrease and increase of rDNA repeats. FOB1 was shown previously to be required for replication fork blocking (RFB) activity at RFB site in rDNA and for recombination hot-spot (HOT1) activity. Thus, DNA replication fork blockage appears to stimulate recombination and play an essential role in rDNA expansion/contraction and sequence homogenization, and possibly, in the instability of repeated sequences in general. RNA Pol I, on the other hand, appears to control repeat numbers, perhaps by stabilizing rDNA with the normal repeat numbers as a stable nucleolar structure.
authors.affiliation: National Institute for Basic Biology, Myodaijicho, Okazaki, 444-8585, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kobayashi
authors.forename: D J
authors.initials: DJ
authors.lastname: Heck
authors.forename: M
authors.initials: M
authors.lastname: Nomura
authors.forename: T
authors.initials: T
authors.lastname: Horiuchi
mesh_terms: D015139:Blotting, Southern; D002455:Cell Division; D002875:Chromosomes / Q000235:genetics; D004261:DNA Replication; D004271:DNA, Fungal / Q000235:genetics / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins; D016521:Electrophoresis, Gel, Pulsed-Field; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D005784:Gene Amplification / Q000235:genetics*; D018628:Gene Dosage; D005822:Genetic Vectors; D008957:Models, Genetic; D008970:Molecular Weight; D016254:Mutagenesis, Insertional; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism*; D011995:Recombination, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D020080:Tandem Repeat Sequences
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C105579:FOB1 protein, S cerevisiae; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D012318:RNA Polymerase I