The donor yeast strain YAC23 containing a 340 kb human genomic DNA fragment in YAC (Yeast Artificial Chromosome) was mated with recipient strain YLB504 by means of improved kar cross and the condidate YACductants were assayed by PCR and the amplification band of 404 bp indicated that they were the same as those of recipient strains (i.e. MAT alpha). Further analysis of the electrokaryotype of the candidate YACductants by PFGE (Pulsed Field Gel Electrophoresis) confirmed that the YACs had succeeded in entering into the recipient cells. The YACs had thus completed the process of transferring from one host to the other.