Table 1.

tsRNAs species

Classification	Subtype	Biogenesis	Characteristics
tRFs	1-tRFs [20]	Cut the 3ʹ end of pre-RNA in the nucleus by RNase Z	Single-stranded, 16–48nt, with poly-U at the end, without redundant sequences of tRNA, distributed in the nucleus and cytoplasm
	2-tRFs [2]	Produced under hypoxic conditions from tRNAGlu, tRNAAsp, tRNAGly, and pre-tRNATyr	Only four types, containing complete anticodon stem and anticodon loop
	3-tRFs [21]	From mature tRNA 3ʹ end. Part of 3-tRFs are produced by angiogenin cleaving the TψC loop of tRNA	Containing RNA polymerase III promoter B box and the CCA sequence, including tRF-3a (18nt) and tRF-3b (22nt)
	5-tRFs [21]	From mature tRNA 5ʹ end	Containing RNA polymerase III promoter A box, including tRF-5a (14–16nt), tRF-5b (22–24nt), and tRF-5 c (28–30nt)
	i-tRFs [22]	From mature tRNA inside	Starting from the second or more downstream nucleotide at mature tRNA 5ʹ end, spaning the anticodon, and extending to the T-loop farthest
tiRNA [12,23]	3ʹ-tiRNA	Produced by angioge-nin in mammalian cell (RNY1 in yeast) cutting the mature tRNA anticodon loop	From tRNA 3ʹ end to the cutting position of anticodon loop
	5ʹ-tiRNA		From tRNA 5ʹ end to the cutting position of anticodon loop