Two Different cis-Active Elements Transfer the Transcriptional Effects of Both EGF and Phorbol Esters

Short cis-active sequences of the rat prolactin or Moloney murine leukemia virus genes transfer transcriptional regulation by both epidermal growth factor and phorbol esters to fusion genes. These sequences act in a position- and orientation-independent manner. Competitive binding analyses with nuclear extracts from stimulated and unstimulated cells suggest that different trans-acting factors associate with the regulatory sequence of each gene. A model is proposed suggesting that both epidermal growth factor and phorbol esters stimulate the transcription of responsive genes via discrete classes of hormone-dependent, enhancer-like elements that bind different trans-acting factors, even in the absence of hormone stimulation.