The PHO84 gene in Saccharomyces cerevisiae encodes a Pi transporter, mutation of which confers constitutive synthesis of repressible acid phosphatase (rAPase), in medium containing repressible amounts of Pi, and an arsenate-resistant phenotype. We selected an arsenate-resistant mutant showing the constitutive synthesis of rAPase on nutrient plates containing 4.5 mM arsenate. This mutant has double mutations designated as pho86 and pho87. The mutant transcribes PHO84 even in the repressible condition but has a severe defect in Pi uptake. The constitutive rAPase+ phenotype of the pho86 pho87 mutant was partially suppressed by an increased dosage of the PHO84 gene. The PHO87 gene was found to be identical with YCR524, according to the published nucleotide sequence of chromosome III, which encodes a protein of 923 amino-acid residues with a highly charged N-terminal half followed by a C-terminal half consisting of 12 membrane-spanning segments as in Pho84p. These and the other findings suggest that the Pho86p and Pho87p proteins collaborate with Pho84p in Pi uptake.