Transcription factors AP‐3 and AP‐2 interact with the SV40 enhancer in a mutually exclusive manner.

The ‘core’ sequence is critical for efficient transcriptional activity of the SV40 enhancer. Moreover, the core was shown to be involved in a signal transduction pathway elicited by treatment of cells with phorbol ester tumor promoters. We report here the identification and characterization of activator protein‐3 (AP‐3), which recognizes the core element. AP‐3 was purified to near homogeneity and identified as a 48K polypeptide. The purified protein is an efficient transcriptional activator in vitro. In addition, we show that AP‐3 and a second factor that recognizes the SV40 enhancer, AP‐2, interact in a mutually exclusive manner. These studies should facilitate understanding of the mechanism by which the SV40 enhancer achieves its characteristic broad cell‐type specificity.