Lepidopteran cell variants resistant to 5-bromodeoxyuridine and their use for transfection of the HSV-TK gene

Following mutagenesis of cultured lepidopteran cells (Spodoptera frugiperda) by ethylmethanesulfonate, three variants resistant to 5-bromodeoxyuridine (BrdUrd) were isolated. These clones were 100- to 200-fold more resistant to BrdUrd than the parental cells and were shown to be deficient in thymidine kinase (TK). The drug-resistant phenotype was stable for up to three years of culture under nonselective conditions. It was also found that the S. frugiperda cell line was highly resistant to aminopterin. A selective medium was formulated and used to select herpes simplex virus thymidine kinase (HSV-TK) transfectants from the TK-deficient cells.