RESCUE OF A SINGLE YEAST ARTIFICIAL CHROMOSOME FROM A COTRANSFORMATION EVENT UTILIZING SEGREGATION AT MEIOSIS

During the construction of yeast artificial chromosome (YAC) libraries to facilitate mapping of the human genome, two YACs may be cotransfor med into the same yeast cell, making further analysis very difficult. We present a simple method to rescue the required YAC that utilizes th e segregation of chromosomes at meiosis. In brief, we crossed the cotr ansformed yeast cell with a non-YAC-containing strain and induced the resulting diploid to sporulate and undergo meiosis. The new haploid ge neration included some yeast cells that contained only the desired YAC . These YACs were analyzed by conventional methods. To exclude the pos sibility that major rearrangement occurred during the procedure, we an alyzed the YACs with restriction enzymes that cut only rarely. We conc lude that this is a useful technique to rescue cotransformed YACs.