A mammalian host-vector system that regulates expression and amplification of transfected genes by temperature induction.

SV40-transformed simian cells that permit temperature-dependent regulation of vector DNA replication were isolated and characterized. These cell lines (ts COS cells) produce high levels of thermolabile large T antigen under the transcriptional control of the Rous sarcoma virus long terminal repeat. The ts COS cell lines can complement SV40 A gene mutants and support replication of SV40-origin containing vectors at 33 degrees C but not at 40 degrees C. It should now be possible to regulate the copy number of transfected plasmid DNA's and also maintain selectable vector sequences either as integrated DNA or as autonomously replicating episomes by modulating T antigen activity in ts COS cells.