Function of yeast and amphioxus tRNA ligase in IRE1alpha-dependent XBP1 mRNA splicing

► Yeast TRL1 functions as an RNA ligase for human XBP1 mRNA splicing in vitro. ► Amphioxus RNL functions as an RNA ligase for human XBP1 mRNA splicing in vitro. ► HSPC117 is not necessary for exon-exon ligation in animal XBP1 mRNA splicing.