TPD1 OF SACCHAROMYCES-CEREVISIAE ENCODES A PROTEIN PHOSPHATASE 2C-LIKE ACTIVITY IMPLICATED IN TRANSFER-RNA SPLICING AND CELL-SEPARATION

The Saccharomyces cerevisiae TPD1 gene has been implicated in tRNA splicing because a tpd1-1 mutant strain accumulates unspliced precursor tRNAs at high temperatures (W. H. van Zyl, N. Wills, and J. R. Broach, Genetics 123:55-68, 1989). The wild-type TPD1 gene was cloned by complementation of the tpd1-1 mutation and shown to encode a protein with substantial homology to protein phosphatase 2C (PP2C) of higher eukaryotes. Expression of Tpd1p in Escherichia coli results in PP2C-like activity. Strains deleted for the TPD1 gene exhibit multiple phenotypes: temperature-sensitive growth, accumulation of unspliced precursor tRNAs, sporulation defects, and failure of cell separation during mitotic growth. On the basis of the presence of these observable phenotypes and the fact that Tpd1p accounts for a small percentage of the observed PP2C activity, we argue that Tpd1p is a unique member of the PP2C family.