Initiation of Ageing Process by Meiotic and Mitotic Recombination within the Ribosomal DNA Genes in Saccharomyces cerevisiae

In the budding yeast of Saccharomyces cerevisiae the tandem repeated of rDNA genes are located onchromosome XII, which is in the nucleolus. There are different types of proteins in the nucleoluskeleton,silencing proteins have got important role in nucleolus.It is shown that meiotic recombination between nonsister chromatids in the rDNA genes are stronglysuppressed, and suggested that silencing proteins such as SIR2 are involved in silencing state. It is alsoshown that nucleolus shows some changes during ageing process. It is claimed that intrachromosomalrecombination within the rDNA repeated sequences; producing 3-μm rDNA circles are accumulated with oldcell. This study looked at the rDNA breakage in two different types of strain ORD 1181 according to theirage. The fine analysis of the rDNA array was performed using restriction endonuclease enzymes, whichdo not cleave within the rDNA array. The results suggest that there are only meiotic hot regions for chromosome breakage in the old cells within the rDNA array.