RESUMEN
Chromosome engineering enables large-scale genome manipulation and can be used as a novel technology for breeding of yeasts. PCR-mediated chromosome splitting (PCS) offers a powerful tool for chromosome engineering by enabling a yeast chromosome to be split at any desired site. By applying PCS, a huge variety of chromosome combinations can be created and the best strain under specific conditions can be selected-a technology that we have called genome reorganization. Once the optimal strain is obtained, chromosome constitutions need to be maintained stably; however, mini-chromosomes of less than 50 kb are at relatively high frequency lost during cultivation. To overcome this problem, in this study we screened for multicopy suppressors of the high loss of mini-chromosomes by using a multicopy genomic library of Saccharomyces cerevisiae. We identified a novel gene, YCR041W, that stabilizes mini-chromosomes. The translational product of YCR041W was suggested to play an important role in increasing stability for mini-chromosome maintenance, probably by decreasing the rate of loss during mitotic cell division. The stabilization of mini-chromosomes conferred by YCR041W overexpression was completely dependent on the silencing protein Sir4, suggesting that a process related to telomere function might be involved in mini-chromosome stabilization. Overexpression of YCR041W stabilized not only a yeast artificial chromosome vector, but also a mini-chromosome derived from a natural chromosome. Taking these results together, we propose that YCR041W overexpression can be used as a novel chromosome engineering tool for controlling mini-chromosome maintenance and loss.