Northern blot analysis was performed as described previously (44 (link)). Briefly, total RNA (500 ng) was resolved by 12% PAGE containing 7 M urea, transferred to Hybond N+ membranes (GE Healthcare) and hybridized to 5΄-end labeled antisense probes (cyto tRNALysCUU: 5΄-GTCTCATGCTCTACCGACT-3΄; cyto tRNAAlaAGC: 5΄-GCGCTCTACCACTGAGCTA-3΄; and mt tRNAValUAC: 5΄-GTGTTAAGCTACACTCTG-3΄). Typhoon 9400 and ImageQuant ver. 5.2 (GE Healthcare) were used for storage phosphor autoradiography visualization and quantification.