THE TYPE OF BASAL PROMOTER DETERMINES THE REGULATED OR CONSTITUTIVE MODE OF TRANSCRIPTION IN THE COMMON CONTROL REGION OF THE YEAST GENE PAIR GCY1 RIO1/

The yeast genes, GCY1 and RIO1, are transcribed divergently from the 8 69-base pair intergenic region, GCY1 is inducible by galactose about 2 5-fold due to Gal4p-binding to a single UAS(GAL), whereas RIO1 is cons titutively expressed, GCY1 has a TATA box obeying the consensus TATAAA , whereas the RIO1 5'-upstream region lacks such a motif. In vitro mut agenesis of the TATA motif of GCY1, on the one hand, and introduction of a TATA-element into the promoter of RIO1, on the other hand, as wel l as inversion of the intergenic region have revealed that transcripti on of GCY1 and RIO1 is only regulated by Gal4p when a consensus TATA m otif is included in their core promoters but not in its absence, The d ata imply that only transcription complexes that assemble at a consens us TATA box are compatible with specific transactivators, such as Gal4 p. As a result, the adjacent gene is subject to regulated expression. By contrast, if a consensus TATA sequence is absent, the initiation co mplex does not respond to regulatory transcription factors, and conseq uently, the respective gene is constitutively transcribed. On the othe r hand, we show that two blocks of homo-oligomeric (dA.dT) sequences d o not function as boundary sequences that might confine regulatory act ion of Gal4p to GCY1.