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Eukaryotic Cell doi:10.1128/EC.00257-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Differential regulation and substrate preferences in two peptide transporters of Saccharomyces cerevisiae

Department of Microbiology, University of Tennessee, Knoxville, TN 37996-0845; Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, CUNY, NY 10314; Graduate School and University Center, CUNY, NY; and The Leonard and Esther Kurtz Term Professor at the College of Staten Island

^* To whom correspondence should be addressed. Email: jbecker{at}utk.edu.

	Abstract

Dal5p has been shown previously to act as an allantoate/ureidosuccinate permease and to play a role in the utilization of certain dipeptides as a nitrogen source in S. cerevisiae. Here, we provide direct evidence that dipeptides are transported by Dal5p, although the affinity of Dal5p for allantoate and ureidosuccinate is higher than that for dipeptides. Allantoate, ureidosuccinate, and to a lesser extent allantoin competed with dipeptide transport by reducing the toxicity of the peptide Ala-Eth and decreasing the accumulation of [¹⁴C]Gly-Leu. In contrast to the well-studied di/tri-peptide transporter Ptr2p whose substrate specificity is very broad, Dal5p preferred to transport non-N-end rule dipeptides. S. cerevisiae W303 was sensitive to the toxic peptide Ala-Eth (non-N-end rule peptide) but not Leu-Eth (N-end rule peptide). Non-N-end rule dipeptides showed better competition with the uptake of [¹⁴C]Gly-Leu than N-end rule dipeptides. Similar to the regulation of PTR2, DAL5 expression was influenced by the addition of Leu and by the CUP9 gene. However, DAL5 expression was down-regulated in the presence of leucine and the absence of CUP9, whereas PTR2 was up-regulated. Toxic dipeptide and uptake assays indicated that either Ptr2p or Dal5p was predominantly used for dipeptide transport in the common laboratory strains S288c and W303, respectively. These studies highlight the complementary activities of two dipeptide transport systems under different regulatory controls in common laboratory yeast strains suggesting that dipeptide transport pathways evolved to respond to different environmental conditions.