Arc1p is required for cytoplasmic confinement of synthetases and tRNA

In yeast, Arc1p interacts with ScMetRS and ScGluRS and operates as a tRNA-Interacting Factor (tIF) in trans of these two synthetases. Its N-terminal domain (N-Arc1p) binds the two synthetases and its C-terminal domain is an EMAPII-like domain organized around an OB-fold-based tIF. ARC1 is not an essential gene but its deletion (arc1(-) cells) is accompanied by a growth retardation phenotype. Here, we show that expression of N-Arc1p or of C-Arc1p alone palliates the growth defect of arc1(-) cells, and that bacterial Trbp111 or human p43, two proteins containing EMAPII-like domains, also improve the growth of an arc1(-) strain. The synthetic lethality of an arc1(-) los1(-) strain can be complemented with either ARC1 or LOS1. Expression of N-Arc1p or C-Arc1p alone does not complement an arc1(-) los1(-) phenotype, but coexpression of the two domains does. Our data demonstrate that Trbp111 or p43 may replace C-Arc1p to complement an arc1(-) los1(-) strain. The two functional domains of Arc1p (N-Arc1p and C-Arc1p) are required to get rid of the synthetic lethal phenotype but do not need to be physically linked. To get some clues to the discrete functions of N-Arc1p and C-Arc1p, we targeted ScMetRS or tIF domains to the nuclear compartment and analyzed their cellular localization by using GFP fusions, and their ability to sustain growth. Our results are consistent with a model according to which Arc1p is a bifunctional protein involved in the subcellular localization of ScMetRS and ScGluRS via its N-terminal domain and of tRNA via its C-terminal domain.