The functional activity of the rat c-Ha-ras promoter requires the coordinate involvement of multiple elements.

Promoter activity in the rat c-Ha-ras promoter region was assessed in NIH 3T3 cells using the chloramphenicol acetyltransferase (CAT) reporter gene. Promoter activity was orientation dependent. Deletion of the GC box closet to the transcriptional start site, or the upstream GC box and the two CAAT boxes, greatly diminished promoter activity. The GC boxes in the SV40 early promoter could not functionally replace the downstream c-Ha-ras GC box, but specifically competed for expression of rat c-Ha-ras promoter activity. Serum-stimulated growth of 3T3 cells stably transfected with p035-ras-CAT was not associated with increased promoter activity. These data indicate that the GC and CAAT boxes in the rat c-Ha-ras gene are related to constitutive, and not regulatory, promoter activity, and that these elements are involved in a coordinate manner.