Competence for DNA transfer of ouabain resistance and thymidine kinase: clonal variation in mouse L-cell recipients.

We have used the calcium phosphate precipitation technique to study the competence of mammalian cell recipients for transformation with genomic mammalian cell DNA. The transformation efficiency for thymidine kinase (tk) varies 10- to 20-fold (up to 10(-4) transformants/recipient) among different subclones of the LM tk- CL 1D mouse fibroblast cell line. Analysis of this phenotype among second-generation subclones indicates that subclones exhibiting high competence tend to breed true, whereas those with low competence do not. Isolation of Tk- revertants from TK+ transformants results in the selection of cells with a high-competence phenotype as measured by their subsequent transformation for tk. This phenotype appears to be a general characteristic of such cells because recipients more competent for transfer of a second marker, ouabain resistance (ouaR). This codominant marker coding for the Na K+-ATPase can be transferred at frequencies of 10(-5) in the high-competence recipients. These results indicate that competence for DNA-mediated gene transfer can be determined in part by genetic factors.