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 on chromosome 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 non-sister chromatids in the rDNA genes are strongly suppressed, and suggested that silencing proteins such as SIR2 are involved in silencing state. It is also shown that nucleolus shows some changes during ageing process. It is claimed that intrachromosomal recombination within the rDNA repeated sequences; producing 3-mm rDNA circles are accumulated with old cell. This study looked at the rDNA breakage in two different types of strain ORD 1181 according to their age. The fine analysis of the rDNA array was performed using restriction endonuclease enzymes, which do 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.