An oligopeptide transport gene from Candida albicans

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Abstract
A Candida albicans oligopeptide transport gene, OPT1, was cloned from a C. albicans genomic library through heterologous expression in the Saccharomyces cerevisiae di-/tripeptide transport mutant PB1X-9B. When transformed with a plasmid harbouring OPT1, S. cerevisiae PB1X-9B, which did not express tetra-/pentapeptide transport activity under the conditions used, was conferred with an oligopeptide transport phenotype, as indicated by growth on the tetrapeptide Lys-Leu-Leu-Gly, sensitivity to toxic tetra- and pentapeptides, and an increase in the initial uptake rate of the radiolabeled tetrapeptide Lys-Leu-Gly-[3H]Leu. The level of oligopeptide transport was found to be influenced in the heterologous host by the source of nitrogen used for growth. The entire 3.8 kb fragment containing the oligopeptide transport activity was sequenced and an ORF of 2349 nucleotides containing a 58 nucleotide intron was identified. The deduced protein product of 783 amino acid residues contained 12 hydrophobic regions suggestive of a membrane transport protein. Sequence comparisons revealed that similar proteins are encoded by genes from S. cerevisiae and Schizosaccharomyces pombe and that OPT1 is not a member of the ABC or PTR membrane transport families.