REGULATION OF THE ADE2 GENE FROM SACCHAROMYCES-CEREVISIAE

Regulation of ADE2 gene expression was investigated in the yeast S. ce revisiae using translational fusions between this gene and the lacZ ge ne from E. coli. Expression was repressed in the presence of adenine a nd slightly increased under amino-acid starvation conditions. The prom oters of the ADE2 gene, and of other genes involved in adenine biosynt hesis, contain the hexanucleotide sequence TGACTC. A search for the he xanucleotide TGACTC in yeast promoter sequences revealed that many gen es not related to amino-acid biosynthesis contain such sequences. We s how here that these elements play a crucial role in ADE2 regulation si nce mutations in two such elements drastically reduced gene expression . Maximal expression required the transcriptional activators Bas1, Bas 2 and Gcn4, whereas Yap1 had only minor effects.