Cotransfer of two linked human genes into cultured mouse cells

Two linked human genes which code for the expression of cytosol thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.75) and galactokinase (ATP:D-galactose 1-phosphotransferase, EC 2.7.1.6) have been cotransferred via purified metaphase chromosomes from the human lymphoblastoid cell line WI-L2a, into mouse L-cells [B82 and LM(TK-)]. Both genes have previously been shown to be closely linked on the human chromosome E17, band q21-22. Coexpression of both human enzyme markers was detected in two out of eight gene transfer clones, whilst the remaining six clones contained only human cytosol thymidine kinase, as shown by electrophoretic techniques. A further 23 human enzyme markers corresponding to 15 different human chromosomes were found to be absent in these gene transfer clones. No human chromosome or chromosomal fragment could be detected by karyotype analyses. Some of the gene transfer clones rapidly lost the transferred donor material when grown in nonselective medium, whereas others expressed a stable phenotype under these conditions. Prolonged maintenance in selective medium favors the survival of gene transfer cells expressing a stable phenotype. Possibly these cells harbor the donor genes integrated into a recipient chromosome.