The effect of replication initiation on gene amplification in the rDNA and its relationship to aging.
In eukaryotes, the ribosomal DNA (rDNA) consists of long tandem repeat arrays. These repeated genes are unstable because homologous recombination between them results in copy number loss. To maintain high copy numbers, yeast has an amplification system that works through a pathway involving the replication fork barrier site and unequal sister chromatid recombination. In this study, we show that an active replication origin is essential for amplification, and the amplification rate correlates with origin activity. Moreover, origin activity affects the levels of extrachromosomal rDNA circles (ERC) that are thought to promote aging. Surprisingly, we found that reduction in ERC level results in shorter life span. We instead show that life span correlates with rDNA stability, which is preferentially reduced in mother cells, and that episomes can induce rDNA instability. These data support a model in which rDNA instability itself is a cause of aging in yeast.
Ganley
Austen R D
AR
National Institute of Genetics, Sokendai-Mishima, Japan.
Ide
Satoru
S
Saka
Kimiko
K
Kobayashi
Takehiko
T
D000375:Aging / Q000235:genetics; D002455:Cell Division / Q000235:genetics*; D004261:DNA Replication; D004270:DNA, Circular / Q000378:metabolism; D004275:DNA, Ribosomal / Q000096:biosynthesis*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005784:Gene Amplification; D015966:Gene Expression Regulation, Fungal; D042822:Genomic Instability; D007700:Kinetics; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011995:Recombination, Genetic; D018741:Replication Origin; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D012854:Sister Chromatid Exchange
D004270:DNA, Circular; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; C105579:FOB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins