Relationship between polyserase-3 and other serine proteases. A, sequence comparison of the serine protease domains of polyserase-3 with other related proteins. Active site amino acids are marked with a black dot. Pol3Spd, pol2Spd and pol1Spd indicate the different serine protease domains of each polyserase. B, phylogenetic tree of different human serine proteases related to polyserase-3. The analysis was performed using the serine protease domain of each enzyme and the Phylogenic Interface Environment program supplied by the Human Genome Mapping Project. C, organization of the human polyserase-3 gene and comparison with other serine protease genes. Relative positions of each exon are indicated by boxes. In the case of matriptase, only the exon/intron organization of its serine protease domain is represented. H, D and S refer to positions of the codons that encode the catalytic triad amino acids in each protease gene.