A suppressor of transcriptional activity is present upstream from the rat c-Ha-ras promoter

We report the presence of an element in the rat c-Ha-ras 5'-flanking region that has a suppressive effect on the promoter of this gene. Promoter activity was determined using constructs of different regions of the c-Ha-ras 5'-flanking region linked to the reporter gene chloramphenicol acetyl transferase (CAT) transfected into NIH-3T3 cells. The presence of the tract 400 base-pairs upstream from the promoter region reduced promoter activity tenfold. This suppressor element was effective in either orientation and was not produced by other DNA fragments of similar length. Transfection with different amounts of plasmid suggested that a trans-acting factor in limiting amounts was acting on the suppressor region. Gel-retardation assays demonstrated that a nuclear protein was present in 3T3 cells that specifically interacted with the 400-base fragment containing the suppressor element.