Multiple sequence alignment of selected splicing endonucleases. Identical and homologous residues are highlighted in green and cyan, respectively. The completely conserved tyrosine is indicated by red lettering highlighted in yellow. The secondary structural elements determined for HsSen15(36–157) and MJ_endo are shown above and below the alignment respectively. Swiss-Prot ID: HsSen15, Q8WW01; ScSen15, Q04675; SpSen15, Q7LKV3; ST_endo2, Q975V0; HsSen34, Q9BSV6; ST_endo1, Q975R3 ; MJ_endo, Q58819. The two red asterisks represent the start and end of the protein product HsSen15(36–157).