Transfer of YAC Clones to New Yeast Hosts

Yeast artificial chromosome (YAC) clones are propagated in yeast, a host organism with a variety of established techniques for altering DNA sequences by homologous recombination in vivo. The modification of existing YAC clones allows the removal of undesired insert DNA (e.g., neighboring coding sequences or chimeric segments), the introduction of new selectable markers, or the replacement of wild-type DNA with defined mutant alleles. To use existing vector systems for YAC manipulation by homologous recombination, transfer to other yeast hosts is often necessary. The development of alternative host strains has been motivated in part by the paucity of nonreverting genetic markers in the genotype of the common library host AB1380 (1 ). In addition, clones with unstable inserts may be more faithfully propagated in recombination-deficient yeast strains (see , e.g., 2 –4 ).