We have constructed recombinant DNA plasmids which carry both the aminoglycoside phosphotransferase (aph) gene and the chloramphenicol acetyl-transferase (CAT) gene linked to the human normal or mutant T24 H-ras1 promoter. We have transfected these plasmids into rat 208F fibroblasts using the calcium phosphate technique and selected for stable transformants by geneticin resistance. These transformants expressed CAT activity at low levels. However, when treated with the phorbol ester TPA, CAT levels increased substantially. Cells transfected with recombinant plasmids carrying a promoterless CAT gene did not respond to TPA. We have noted four motifs in the H-ras1 promoter region which resemble TPA-inducible and AP-1-binding consensus sequences. We suggest that AP-1-like proteins may play a role in control of H-ras1 transcription.
