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

We have transferred DNa to Chinese hamster ovary (CHO) cells by DNA-mediated transformation. CHO tk- cells were transformed with the clones 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 x 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.