AN OLIGOPEPTIDE TRANSPORT GENE FROM CANDIDA-ALBICANS

A Candida albicans oligopeptide transport gene, OPT1. was cloned from a C. albicans genomic library through heterologous expression in the S accharomyces cerevisiae di-/tripeptide transport mutant PB1X-9B. When transformed with a plasmid harbouring OPT1, S. cerevisiae PB1X-9B, whi ch did not express tetra-/pentapeptide transport activity under the co nditions used, was conferred with an oligopeptide transport phenotype, as indicated by growth on the tetrapeptide Lys-Leu-Leu-Gly, sensitivi ty to toxic tetra- and pentapeptides, and an increase in the initial u ptake rate of the radiolabelled tetrapeptide Lys-Leu-Gly-[H-3]Leu. The level of oligopeptide transport was found to be influenced in the het erologous host by the source of nitrogen used for growth. The entire 3 .8 kb fragment containing the oligopeptide transport activity was sequ enced and an ORF of 2349 nucleotides containing a 58 nucleotide intron was identified. The deduced protein product of 783 amino acid residue s contained 12 hydrophobic regions suggestive of a membrane transport protein. Sequence comparisons revealed that similar proteins are encod ed by genes from S. cerevisiae and Schisosaccharomyces pombe and that OPT1 is not a member of the ABC or PTR membrane transport families.