TRNA-controlled Nuclear Import of a Human tRNA Synthetase

Guangsen Fu,Tao Xu,Yi Shi,Na Wei,Xiang-Lei Yang

doi:10.1074/jbc.c111.325902

Abstract

Aminoacyl-tRNA synthetases, essential components of the cytoplasmic translation apparatus, also have nuclear functions that continue to be elucidated. However, little is known about how the distribution between cytoplasmic and nuclear compartments is controlled. Using a combination of methods, here we showed that human tyrosyl-tRNA synthetase (TyrRS) distributes to the nucleus and that the nuclear import of human TyrRS is regulated by its cognate tRNA(Tyr). We identified a hexapeptide motif in the anticodon recognition domain that is critical for nuclear import of the synthetase. Remarkably, this nuclear localization signal (NLS) sequence motif is also important for interacting with tRNA(Tyr). As a consequence, mutational alteration of the hexapeptide simultaneously attenuated aminoacylation and nuclear localization. Because the NLS is sterically blocked when the cognate tRNA is bound to TyrRS, we hypothesized that the nuclear distribution of TyrRS is regulated by tRNA(Tyr). This expectation was confirmed by RNAi knockdown of tRNA(Tyr) expression, which led to robust nuclear import of TyrRS. Further bioinformatics analysis showed that to have nuclear import of TyrRS directly controlled by tRNA(Tyr) in higher organisms, the NLS of lower eukaryotes was abandoned, whereas the new NLS was evolved from an anticodon-binding hexapeptide motif. Thus, higher organisms developed a strategy to make tRNA a regulator of the nuclear trafficking of its cognate synthetase. The design in principle should coordinate nuclear import of a tRNA synthetase with the demands of protein synthesis in the cytoplasm.

Highlights

Many tRNA synthetases were found in the nucleus of eukaryotic cells where translation does not occur
To address the question of how the distribution of a tRNA synthetase is controlled, we focused on human TyrRS because it is one of the most characterized tRNA synthetases, with crystal structures being solved from 12 different organisms including human (Protein Data Bank (PDB) database)
Through a combination of methods, we identified a distinct nuclear localization signal (NLS) sequence for human TyrRS and showed that this sequence was adapted from a key motif used for tRNA anticodon binding

Summary

Background

Many tRNA synthetases were found in the nucleus of eukaryotic cells where translation does not occur. Using a combination of methods, here we showed that human tyrosyl-tRNA synthetase (TyrRS) distributes to the nucleus and that the nuclear import of human TyrRS is regulated by its cognate tRNATyr. We identified a hexapeptide motif in the anticodon recognition domain that is critical for nuclear import of the synthetase. Through a combination of methods, we identified a distinct NLS sequence for human TyrRS and showed that this sequence was adapted from a key motif used for tRNA anticodon binding. This scenario effectively coordinates nuclear trafficking of the synthetase with its role for protein synthesis in the cytoplasm

EXPERIMENTAL PROCEDURES

The abbreviations used are

RESULTS

DISCUSSION