GENE CONVERSION PLAYS THE MAJOR ROLE IN CONTROLLING THE STABILITY OF LARGE TANDEM REPEATS IN YEAST

The genomic stability of the rDNA tandem array in yeast is tightly con trolled to allow sequence homogenization and at the same time prevent deleterious rearrangements. In our study, we show that gene conversion , and not unequal sister chromatid exchange, is the predominant recomb ination mechanism regulating the expansion and contraction of the rDNA array. Furthermore, we found that RAD52, which is essential for gene conversion, is required for marker duplication stimulated in the absen ce of the two yeast type I topoisomerases. Our results have implicatio ns for the mechanisms regulating genomic stability of repetitive seque nce families found in all eukaryotes.