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Eukaryotic Cell, December 2004, p. 1492-1503, Vol. 3, No. 6
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.6.1492-1503.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Saccharomyces cerevisiae Aqr1 Is an Internal-Membrane Transporter Involved in Excretion of Amino Acids

Isabel Velasco,1 Sandra Tenreiro,2 Isabel L. Calderon,1 and Bruno André3*

Departamento de Genética, Facultad de Biologia, Universidad de Sevilla, Seville, Spain,1 Centro de Engenharia Biológica e Química, Instituto Superior Técnico, Lisbon, Portugal,2 Laboratoire de Physiologie Moléculaire de la Cellule, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles (ULB), Gosselies, Belgium3

Received 18 August 2004/ Accepted 19 August 2004

Excretion of amino acids by yeast cells was reported long ago but has not been characterized in molecular terms. It is typically favored by overproduction of the amino acid and/or impairment of its uptake. Here we describe the construction of a yeast strain excreting threonine and homoserine. Using this excretor strain, we then applied a reverse-genetics approach and found that the transporter encoded by the YNL065w/AQR1 gene, a protein thought to mediate H+ antiport, is involved in homoserine and threonine excretion. Furthermore, overexpression of AQR1 led to increased excretion of several amino acids (alanine, aspartate, and glutamate) known to be relatively abundant in the cytosol. Transcription of the AQR1 gene is induced severalfold by a number of amino acids and appears to be under the negative control of Gcn4. An Aqr1-green fluorescent protein fusion protein is located in multiple internal membrane structures and appears to cycle continuously between these compartments and the plasma membrane. The Aqr1 sequence is significantly similar to the vesicular amine transporters of secretory vesicles of neuronal cells. We propose that Aqr1 catalyzes transport of excess amino acids into vesicles, which then release them in the extracellular space by exocytosis.

* Corresponding author. Mailing address: Physiologie Moléculaire de la Cellule (CP300), Université Libre de Bruxelles (ULB), Institut de Biologie et de Médecine Moléculaires (IBMM), 12 rue des Pr. Jeener et Brachet, 6041 Gosselies, Belgium. Phone: 32-2-6509958. Fax: 32-2-6509950. E-mail: bran{at}ulb.ac.be.

Eukaryotic Cell, December 2004, p. 1492-1503, Vol. 3, No. 6
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.6.1492-1503.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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