A mammalian viral enhancer confers transcriptional regulation in yeast

Transcriptional enhancers are DNA sequences that regulate RNA transcription from linked promoters by binding to cellular proteins (trans-activators). In the mammalian virus SV40, initiation of transcription is controlled, in part, by a strong 72-base pair enhancer. We show that yeast cells contain a factor that binds specifically to a key DNA motif in the SV40 enhancer, the P element that is essential for viral transcription in mammalian cells. The P element shows sequence similarity to a yeast DNA transcriptional regulatory element, GCN4, that controls transcription of genes that code for amino acid biosynthetic enzymes. Insertion of the SV40 enhancer or single or multiple copies of the P element itself upstream from the cytochrome Cyc-1 promoter places the hybrid viral-yeast transcription unit under metabolic control in yeast cells. These studies suggest that the SV40 P element and its complementary trans-activator represent a conserved transcriptional control mechanism that operates on widely divergent functions in evolution.