Transfer of codominant markers by isolated metaphase chromosomes in Chinese hamster ovary cells

Codominant mutations to methotrexate and ouabain resistance in Chinese hamster ovary cells can be transferred to recipient Chinese hamster ovary cells by isolated metaphase chromosomes. For methotrexate, both the structural change and the increased activity of dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase EC 1.5.1.3), characteristic of the donor cells, are observed in the transferents (cells that carry and express functions derived by chromosome transfer). The transferents are unstable in the absence of selection although stable clones can be isolated. From results obtained by fractionation of chromosomes and transfer to recipients, the methotrexate and ouabain markers can be assigned to the middle and large size-classes of chromosomes, respectively. By fractionation and transfer of chromosomes, from transferents to new recipients, evidence has been obtained that chromosome integration is not restricted to a particular chromosomal site in the recipient.