Fig. 1

Biogenesis and classification of tRFs. Pre-tRNAs are first transcribed from tRNA genes by RNA polymerase III in the nucleus, followed by cleavage of RNase P and RNase Z at the 5’ and 3’ ends, respectively. The pre-tRNAs undergo splicing of intron by tRNA endonucleases, attachment of CCA sequence at 3’ end and further modifications to achieve tRNA maturation. Based on the incision site of mature tRNAs, tRFs can be divided into 5’-halves, 3’-halves, 5’-tRFs, 3’-tRFs, and i-tRFs. The cleavage of pre-tRNAs also generates tRFs