Comparison of Bm-SPN-2 with other serpins: human 1-antitrypsin (1-AT), C elegans serpin (Ce-spn), chicken gene Y protein (gene Y), mouse proteinase inhibitor 3 (SPI3), and human squamous cell carcinoma antigen 1 (SCCA1). (A) Amino acid sequences: the alignment of amino acid sequences using PILEUP and BOXSHADE programs was based on the 1-AT crystal structure35 40 in which the conserved helices and strands are defined and was manually adjusted to give the best fit. Gaps were introduced in sequences for optimal alignment. The 1-AT sequence is given without the signal sequence (MPSSVSWGILLLAGLCCLVPVSLA). Identical residues are highlighted in black and similar residues in gray shading. The 51 starred residues are those categorized as conserved in the larger serpin superfamily. The scissile bond is marked with an arrow. (B) Intron/exon positions in serpins. Thick lines indicate coding regions, thin lines indicate untranslated regions, and gaps have been introduced to optimize alignment; arrows marked by uppercase letters indicate positions of introns. Sequences were aligned on the basis of amino acid similarity with the scale showing amino acid positions beginning with the first methionine of Bm-SPN-2. Introns are shaded according to their phase: open (phase 0), shaded (phase 1), and solid (phase 2). Vertical lines connect introns considered to be in identical positions.