The role of acentric chromosome fragments in gene amplification.

We assessed the role of acentric chromosome fragments in gene amplification by using cell fusion techniques to introduce the fragmented chromosomes of a donor Chinese hamster ovary (CHO) cell line that contained the dihydrofolate reductase (dhfr) gene(s) into a CHO cell line deficient for dhfr. Chromosome fragments were successfully integrated into cells at a frequency of approximately 3%. Methotrexate-resistant variants arose much more frequently in two cell lines derived from these successful cell fusions than in wild-type CHO cells. The hybrid cell lines also amplified their dhfr genes more readily than did the CHO cell line used as dhfr donor.