Rap1p is a negative regulator of the RAP1 gene

The promoter of the RAP1 gene contains four potential binding sites for Rap1p, located between the UAS and the RNA initiation site. We have confirmed that three of these sites are recognised by Rap1p in vitro. Different combinations of the three sites were then mutated to abolish Rap1p binding, and the effect of these mutations on promoter activity was determined. When all three Rap1p sites were mutated, the activity of the promoter increased by about 130%, indicating that at least one of the sites is a negative element. Analysis of promoters with different combinations of the mutant sites revealed that the 5'-most site (A) is the principal target for repression. To test the involvement of Rap1p in controlling RAP1 expression, we have measured transcription of the chromosomal RAP1 gene in a RAP1 wild-type strain and two strains containing rap1ts mutations. At a semi-permissive temperature, the RAP1 promoter was more active in the rap1ts strains than in the RAP1 wild-type strain, suggesting that expression of the chromosomal RAP1 gene is greater when the activity of Rap1p in the cell is compromised. The activities of the wild-type promoter, and the promoter with mutations in the three Rap1p-binding sites, were compared in sir1, sir2, sir3 and sir4 mutant strains. In each case, the mutated promoter was significantly more active than the wild-type promoter, implying that the repression mechanism is not dependent on any one of the SIR gene products.