**3. tsRNA**

Previously thought of as simple degradation products, tsRNA are cleaved fragments of full tRNA transcripts. In eukaryotes, tRNA genes are transcribed by polymerase III and the 5′ leader sequence and 3′ trailer sequences are removed from the pre-tRNA sequence by the endonucleases RNase P and RNase Z, respectively [42–44]. The mature tRNA is generated by the addition of a CCA tail by CCase [45, 46]. Mature tRNAs are 73–90 nt long with a classic 'cloverleaf' secondary structure consisting of an anti-codon loop that recognizes mRNA codons, an acceptor stem that binds amino acids, a dihydrouridine (D) loop, a thymidine (T) loop and a variable (V) loop [47]. tRNA are a highly modified species with over 170 independent modifications reported to date [48]. These modifications are largely localized on the anticodon loop, affecting the speed and accuracy of decoding, or the structural core of the molecule affecting stability and degradation pathways [49, 50]. tsRNA are generated from the cleavage of tRNA by endonucleases and are classified by their cleavage site and length as either tRNA-derived stress-induced RNA (tiRNA) or tRNA fragments (tRFs).
