Replication fork block protein, Fob1, acts as an rDNA region specific recombinator in S. cerevisiae.
BACKGROUND
The analysis of homologous recombination in the tandemly repeating rDNA array of Saccharomyces cerevisiae should provide useful information about the stability of not only the rDNA repeat but also the abundant repeated sequences on higher eukaryotic genomes. However, the data obtained so far are not yet conclusive, due to the absence of a reliable assay for detecting products of recombination in the rDNA array.


RESULTS
We developed an assay method to detect the products of unequal sister-chromatid recombination (marker-duplication products) in yeast rDNA. This assay, together with the circular rDNA detection assay, was used for the analysis. Marker-duplication occurred throughout the rDNA cluster, preferentially between nearby repeat units. The FOB1 and RAD52 genes were required for both types of recombinant formation. FOB1 showed a gene dosage effect on not only the amounts of both recombinants, but also on the copy number of the repeat. However, unlike the RAD52 gene, the FOB1 gene was not involved in homologous recombination in a non-rDNA locus. In addition, the marker-duplication products were drastically decreased in the mre11 mutant.


CONCLUSIONS
Our data demonstrate that FOB1- and RAD52-dependent homologous recombination cause the gain and loss of a few copies of the rDNA unit, and this must be a basic mechanism responsible for amplification and reduction of the rDNA copy number. In addition, FOB1 may also play a role in the copy number regulation of rDNA tandem repeats.
Johzuka
Katsuki
K
National Institute for Basic Biology, Nishigonaka 38, Myodaiji-cyo, Okazaki 444-8585, Japan.
Horiuchi
Takashi
T
D004275:DNA, Ribosomal / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004706:Endodeoxyribonucleases / Q000235:genetics; D005090:Exodeoxyribonucleases / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D006655:Histone Deacetylases / Q000235:genetics; D051721:Rad52 DNA Repair and Recombination Protein; D011995:Recombination, Genetic / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D020080:Tandem Repeat Sequences / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C105579:FOB1 protein, S cerevisiae; D005656:Fungal Proteins; C120535:HOT1 protein, S cerevisiae; C497197:RAD52 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; D014157:Transcription Factors; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases