ACPR from Candida albicans encodes a protein antigenically related to the secretory acid proteinase of this yeast. Its amino terminal domain is highly similar to the amino terminal, DNA-binding domain of STE12 of Saccharomyces cerevisiae. STE12 is involved in mating of haploids and in pseudohyphae formation in diploids. ACPR, or its DNA-binding domain swapped into STE12, can support pseudohyphae formation in S. cerevisiae diploids. However, unlike STE12, these constructs affect the budding pattern and induce pseudohyphae formation in S. cerevisiae haploids as well, and this induction is independent of the nitrogen status of the medium. ACPR appears to be a stronger inducer of pseudohyphae than STE12 and is likely to be involved in the formation of pseudohyphae and hyphae in C. albicans.