Genome recombination studies

In the Saccharomyces cerevisiae genome the regions adjacent to the 32 chromosome ends, the subtelomeres, are tethered at the nuclear periphery during vegetative / somatic growth and during sporulation / gametogenesis. This is in contrast to the rest of the genome, the interstitial regions, which are located throughout the nucleus. There is evidence that recombination between different subtelomeres is the exceptionally frequent, but that subtelomeres and interstitial regions do not recombine. These features of recombination involving subtelomeres may result from a structure that interacts with the subtelomeres, partitioning them from interstitial regions. Our aim was to characterise which part of the subtelomeres this recombination barrier interacts with. As a tool for estimating the rate and efficiency of recombination between different regions, a set of insertions into the S. cerevisiae genome was engineered. This set included 11 insertions at regular intervals along the terminal 10% of one chromosome arm, marking an interstitial region and the subtelomere. In addition, insertions were also made into a sample of other subtelomeres and interstitial regions. Both recombination during vegetative growth (mitotic recombination) and during sporulation (meiotic recombination) were assayed, between numerous combinations of these insertions. In agreement with previous studies, our results indicate that recombination between interstitial regions and subtelomeres is less efficient than recombination between different interstitial regions. Moreover, this is true of both mitotic and meiotic recombination. However, our efficiency data indicate this may result from tethering of subtelomeres at the nuclear periphery, rather than a partition in the nucleus. Tethering may suppress recombination between subtelomeres and most interstitial regions, simply by maintaining a large relative distance between these two regions. In contrast, the efficiency of mitotic and meiotic recombination between subtelomeres appear to be very different. Mitotic recombination between different subtelomeres appears to be exceptionally efficient, while meiotic recombination between different subtelomeres appears to be inefficient.