Sequence analysis of pXbp1. (A) After IRE1-mediated splicing, 26 nucleotides were deleted from unspliced pXbp1U mRNA and produced the 378 amino acids spliced pXbp1 protein. Arrow shows the primers used in this study. pXbp1-F1 and pXbp1-R1 were used to amplify the full length of pXbp1 mRNA. pXbp1-SF and pXbp1-SR were used to detect the spliced pXbp1 mRNA. (B) The consensus sequence of the cleavage targets by IRE1α is in gray and the cleavage sites are indicated by arrows. (C) Schematic representation of the cleavage sites with secondary structure were predicted by CentroidFOLD. (D) Amino acid sequence comparisons between the human XBP1 and porcine XBP1 protein using the ClustalW method. Identical amino acid residues are shaded in black and the basic leucine zipper (bZIP) domain is underlined. (E) Phylogenetic trees of XBP1 were generated with the neighbor-joining method.