Chemical footprinting and kinetic assays reveal dual functions for highly conserved eukaryotic tRNA guanylyltransferase residues.

tRNA guanylyltransferase (Thg1) adds a single guanine to the -1 position of tRNA as part of its maturation. This seemingly modest addition of one nucleotide to tRNA ensures translational fidelity by providing a critical identity element for the histidyl aminoacyl tRNA synthetase (HisRS). Like HisRS, Thg1 utilizes the GUG anticodon for selective tRNA recognition, and Thg1-tRNA complex structures have revealed conserved residues that interact with anticodon nucleotides.

A mutation in the THG1L gene in a family with cerebellar ataxia and developmental delay.

Autosomal-recessive cerebellar atrophy is usually associated with inactivating mutations and early-onset presentation. The underlying molecular diagnosis suggests the involvement of neuronal survival pathways, but many mechanisms are still lacking and most patients elude genetic diagnosis. Using whole exome sequencing, we identified homozygous p.