Sen15 (IPR018593), a tRNA-splicing endonuclease subunit. One of this heterotetrameric enzyme's two structural subunits is the Sen15 subunit of the tRNA intron splicing endonuclease. As part of the functional endonuclease assembly, two monomers of Sen15 fold with two monomers of one of the two catalytic subunits, Sen34, to form an α2-β2 tetramer.