Putative GTP-Binding Protein, Gtr1, Associated with the Function of the Pho84 Inorganic Phosphate Transporter in Saccharomyces cerevisiae

Abstract

We have found an open reading frame which is 1.1 kb upstream of PH084 (which encodes a P_i transporter) and is transcribed from the opposite strand. In Saccharomyces cerevisiae, this gene is distal to the TUB3 locus on the left arm of chromosome XIII and is named GTR1. GTR1 encodes a protein consisting of 310 amino acid residues containing, in its N-terminal region, the characteristic tripartite consensus elements for binding GTP conserved in GTP-binding proteins, except for histidine in place of a widely conserved aspargine residue in element III. Disruption of the GTR1 gene resulted in slow growth at 30°C and no growth at 15°C; other phenotypes resembled those of pho84 mutants and included constitutive synthesis of repressible acid phosphatase, reduced P_i transport activity, and resistance to arsenate. The latter phenotypes were shown to be due to a defect in P_i uptake, and the Gtr1 protein was found to be functionally associated with the Pho84 P_i transporter. Recombination between chromosome V (at the URA3 locus) and chromosome XIII (in the GTR1-PH084-TUB3 region) by using a plasmid-encoded site-specific recombination system indicated that the order of these genes was telomere-TUB3-PHO84-GTR1-CEN_XIII.