Tetrapod homologues of Atg4 share several conserved cysteine residues. (A) Amino-acid alignment of the region surrounding the active cysteine residue among members of the Atg4 family. Sequences of the following accession numbers are aligned: BAB83890, BAB83889, NP_777364, NP_777363, NP_001001171, CAG32326, AAH73017, AAH82660, AAH95617, XP_393739, NP_608563, XP_661074, NP_014176 and NP_191554. The alignment was preformed using the ClustalX multiple alignment program and is depicted by the ESPript 2.0 program, representing identity by a black frame and homology by a gray background. Numbering is according to the HsAtg4B sequence. α-Helices and a β-sheet found in this region according to the recently solved structure of HsAtg4B (; ) are marked as black ellipses and a gray arrow, respectively. The catalytic cysteine residue is marked by a wide black arrow; other conserved cysteines are marked by thin black arrows. (B) A phylogenetic tree was created based on the alignment presented in (A) using the NJplot program (). Bootstrap values indicating the reliability of the tree branches (with 1000 being the maximal value) are shown.