Ser-tRNA(Ala) hydrolase; hydrolyzes Ser-mischarged cytoplasmic and mitochondrial tRNAs; regulates translational fidelity based on Ala- and Thr-to-Ser misincorporation in the null mutant; trans-editing factor for alanyl- and threonyl-tRNA synthetases and seryl-tRNA synthetase (SerRS) via hydrolysis; null mutant displays decreased translation rate and increased readthrough of premature stop codons; (GFP)-fusion protein localizes to the cytoplasm; homologous to human trans-editing factor AARSD