Cloning and characterization of the Schizosaccharomyces pombe tRNA : pseudouridine synthase Pus1p

Saccharomyces cerevisiae cells that carry deletions in both the LOS1 (a tRN A export receptor) and the PUS1 (a tRNA:pseudouridine synthase) genes exhib it a thermosensitive growth defect. A Schizosaccharomyces pombe gene, named spPUS1, was cloned from a cDNA library by complementation of this conditio nal lethal phenotype. The corresponding protein, spPus1p, shows sequence si milarity to S.cerevisiae and murine Pus1p as well as other known members of the pseudouridine synthase family. Accordingly, recombinant spPus1p can ca talyze in vitro the formation of pseudouridines at positions 27, 28, 34, 35 and 36 of yeast tRNA transcripts. The sequence and functional conservation of the Pus1p proteins in fungi and mammalian species and their notable abs ence from prokaryotes suggest that this family of pseudouridine synthases i s required for a eukaryote-specific step of tRNA biogenesis, such as nuclea r export.