Neutral selection of transfected mammalian cells using tissue plasminogen activator gene expression

The gene that produces the proteolytic enzyme, tissue plasminogen activator (tPA), was used as a selectable marker for transfection. Cells that were successfully transfected with plasmids containing a gene for tPA (tpa) produce plaques in the caseinolysis assay. Two tpa-containing plasmids were constructed and used to transfect a variety of cell types. One plasmid contained the promoter region of simian virus 40 and the other contained the Moloney murine leukemia virus promoter. No significant difference in transfection frequencies was found for the two plasmids. However, 80% of the cell types tested produced plaques. This system allows for the identification and isolation of transfected cells under conditions that are not lethal to nontransfected cells.