Probable endopeptidase. In tracheal terminal cells, acts downstream of ich to regulate seamless tube growth and/or maintenance probably by processing lumenal matrix proteins. Detected in embryo at stage 13 in the posterior spiracles and foregut primordium. By stage 15, expressed specifically in epithelia secreting cuticle, including the trachea, foregut, hindgut and epidermis. Embryonic lethal. RNAi-mediated knockdown in tracheal terminal cells results in cystic dilations and discontinuities of the apical membrane; terminal cells are severely pruned with terminal branches largely devoid of lumenal membrane, except for isolated inclusions. Belongs to the peptidase S1 family.