An insertion mutation associated with constitutive expression of repressible acid phosphatase in Saccharomyces...

The PHO83 mutation in Saccharomyces cerevisiae, which had been detected on the basis of constitutive production of repressible acid phosphatase and mapped at the end of the PHO5 locus, was analysed by Southern hybridization with cloned DNA fragments of the PHO5 gene as probe. It was shown that this mutant has a DNA insertion of about 6 kilobase pairs, probably in the 5'-noncoding region of the PHO5 gene. Production of repressible acid phosphatase by the PHO83 mutant is partially independent of the function of the PHO2 and PHO4 genes, the positive regulatory genes whose functions are indispensable for PHO5 expression. PHO83 mutants are constitutive in a and alpha cells, either haploid or diploid, but not in non-mating cells, MATa/MAT alpha or a certain sterile mutation. These observations strongly suggest that the PHO83 mutation is caused by insertion of a Ty element in the 5'-noncoding region of the PHO5 gene.