Isolation of an extragenic suppressor of the rnal-1 mutation in Saccharomyces cerevisiae

The small GTPase Ran is essential for nucleocytoplasmic transport of macromolecules. In the yeast Saccharomyces cerevisiae, Rnalp functions as a Ran-GTPase activating protein (RanGAP1). Strains carrying the rnal-1 mutation exhibit defects in nuclear transport and, as a consequence, accumulate precursor tRNAs. We have isolated two recessive suppressors of the rnal-1 mutation. Further characterization of one of the suppressor mutations, srn10-1, reveals that the mutation (i) can not bypass the need for Rnalp function and (ii) suppresses the accumulation of unspliced pre-tRNA caused by rnal-1. The SRN10 gene is not essential for cell viability and encodes an acidic protein (pI = 5.27) of 24.8 kDa. Srn10p is located in the cytoplasm, as determined by indirect immunofluorescence microscopy. Two-hybrid analysis reveals that there is a physical interaction between Srn10p and Rnalp in vivo. Our results identify a protein that interacts with the yeast RanGAP1.