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Journal of Biological Sciences
Year: 2007  |  Volume: 7  |  Issue: 7  |  Page No.: 1092 - 1101

Homologous Recombination Repair Within the rDNA Array in Saccharomyces cerevisiae

M. Motovali-Bashi, Z. Hojati and Richard M. Walmsley    

Abstract: Homologous recombination repair starts with Double-strand Breaks (DSBs) followed by crossing-over and recombination. The expected frequency of meiotic chromosomal exchange in the region of chromosome XII encoding ribosomal DNA in Saccharomyces cerevisiae is 3.5 to 5 events per cell per meiosis. However interchromosomal meiotic recombination in the rDNA gene is very rare, suggesting repression of DSB and crossing-over. On the other hand, mitotic events such as intrachromosomal recombination producing 3 μm rDNA circles (which accumulate with cellular age) and unequal sister chromatid exchanges appear to be quite common. This study looked at the rDNA breakage in the strain ORD 1181, a rad50S mutant with SK1 background, which does a relatively fast and near synchronous meiosis. The fine analysis of the rDNA array was performed using restriction endonuclease enzymes that do not cleave within the rDNA array. The results suggest that there are at least two hot regions for chromosome breakage within the rDNA array. According to our previous studies we suggest that the DSB hot regions are in one homologue. However, there is possibility that other homologue is involving in DSB too.

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