Constitutes one of the two catalytic subunit of the tRNA-splicing endonuclease complex; a complex responsible for identification and cleavage of the splice sites in pre-tRNA. It cleaves pre-tRNA at the 5’- and 3’-splice sites to release the intron. The products are an intron and two tRNA half-molecules bearing 2’;3’-cyclic phosphate and 5’-OH termini. There are no conserved sequences at the splice sites; but the intron is invariably located at the same site in the gene; placing the splice sites an invariant distance from the constant structural features of the tRNA body. It probably carries the active site for 3’-splice site cleavage. The tRNA splicing endonuclease is also involved in mRNA processing via its association with pre-mRNA 3’-end processing factors; establishing a link between pre-tRNA splicing and pre-mRNA 3’-end formation; suggesting that the endonuclease subunits function in multiple RNA-processing events.