Abstract

The enzyme tRNA nucleotidyltransferase catalyzes the addition of CMP and AMP residues to the 3 ' end of immature tRNAs. In eukaryotic cells, the nuclear, mitochondrial and chloroplast genomes all encode tRNAs and tRNA nucleotidyltransferase is therefore required in these compartments as well as in the cytosol. In yeast, one gene codes for the tRNA nucleotidyltransferase that functions in the nucleus, mitochondrion and cytosol. As a single gene coding for tRNA nucleotidyltransferase has been identified in Arabidopsis , we were interested in determining whether its gene product(s) is(are) targeted to multiple locations. Protoplast transformation experiments using a green fluorescent protein:tARNA nucleotidyltransferase fusion protein suggests that, as in yeast, both mitochondrial and nuclear targeting information are encoded by the Arabidopsis tRNA nucleotidyltransferase. In addition, this protein also appears to be targeted to the chloroplast. The Arabidopsis homologue of the yeast Gim1p which has been shown in a yeast two-hybrid assay to interact with the Arabidopsis tRNA nucleotidyltransferase (Gu, 2000), complemented a cold and benomyl-sensitive defect in the yeast GIM1 gene. The two-hybrid interaction between the Arabidopsis Gim1p homologue and the Arabidopsis tRNA nucleotidyltransferase was shown to be dependent on the presence of the yeast Gim5p. This observation may suggest that the interaction between Gim1p and tRNA nucleotidyltransferase requires the G[barbelow]enes I[barbelow]nvolved in M[barbelow]icrotubule assembly C[barbelow]omplex (GIMC) of which both Gim1p and Gim5p are components.