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 (By similarity). pretRNA = a 3'-half-tRNA molecule with a 5'-OH end + a 5'-half-tRNA molecule with a 2',3'-cyclic phosphate end + an intron with a 2',3'-cyclic phosphate and a 5'-hydroxyl terminus. Heterotetramer composed of SEN2, SEN15, SEN34 and SEN54. Interacts directly with SEN15 (By similarity). Belongs to the tRNA-intron endonuclease family.