SCHIZOSACCHAROMYCES-POMBE ISP4 ENCODES A TRANSPORTER REPRESENTING A NOVEL FAMILY OF OLIGOPEPTIDE TRANSPORTERS

We have recently cloned an oligopeptide transport gene from Candida al bicans denoted OPT1. This gene showed significant sequence similarity to three open reading frames (ORFs) with no previously established fun ction: isp4 from Schizosaccharomyces pombe and Saccharomyces cerevisia e YJL212C and YPR194C, identified during the genome project. The S. po mbe gene isp4 was originally identified by Sate ef al. as a gene that was upregulated through nitrogen starvation induction of meiosis. Howe ver, an isp4 Delta strain exhibited a wild-type phenotype with respect to sexual differentiation. We have found that the same isp4 Delta str ain is deficient in tetrapeptide transport activity as measured by its resistance to toxic tetrapeptides, by its inability to accumulate a r adiolabelled tetrapeptide and by the inability to use tetrapeptides as a sole source of an amino acid to. satisfy an auxotrophic requirement . Similarly, we found that the ORF YPR194C from S. cerevisiae encodes an oligopeptide transporter. Sequence analyses as well as physiologica l evidence has led us to propose that the proteins encoded by isp4 and the genes identified from S. cerevisiae and C. albicans comprise a ne w group of transporters specific for small oligopeptides, which we hav e named the OPT family.