The Sen15 subunit of the tRNA intron-splicing endonuclease is one of the two structural subunits of this hetero-tetrameric enzyme. Residues 36-157 of this subunit possess a novel homodimeric fold. Each monomer consists of three alpha-helices and a mixed antiparallel/parallel beta-sheet. Two monomers of Sen15 fold with two monomers of Sen34, one of the two catalytic subunits, to form an alpha2-beta2 tetramer as part of the functional endonuclease assembly.

1: Three-dimensional structure determined for a subunit of human tRNA splicing endonuclease (Sen15) reveals a novel dimeric fold. Song J, Markley JL; J Mol Biol. 2007;366:155-164. PMID:17166513

2: Sequence, structure and functional diversity of PD-(D/E)XK phosphodiesterase superfamily. Steczkiewicz K, Muszewska A, Knizewski L, Rychlewski L, Ginalski K; Nucleic Acids Res. 2012;40:7016-7045. PMID:22638584