Transfer of genes to chinese hamster ovary cells by DNA-mediated transformation

Abstract

We have transferred DNA to Chinese hamster ovary (CHO) cells by DNA-mediated transformation. CHO tk⁻ cells were transformed with the cloned gene for herpes simplex virus thymidine kinase (HSV-tk) and were found to have a 50-fold lower frequency of transformation than mouse Ltk⁻ cells at the same DNA dosage. By altering the amount of tk gene and carrier DNA present, frequencies of up to 5 × 10⁻⁵ were obtained. CHO HSV- tk⁺ transformants were very stable, and in several clones the HSV-tk gene copies integrated in higher-molecular-weight DNA. These cells also exhibited cotransformation for unselected markers. CHO lines were also transformed at a frequency of 10⁻⁴ with the bacterial gene Ecogpt in a SV40-pBR322 vector. CHO tk⁻ cells could be transformed at a frequency of 10⁻⁷ with cellular DNA isolated from CHO tk⁺ cells. CHO cells offer a well-defined genetic system within which to transfer either cloned or whole cellular DNAs.