Two types of serine proteases and a serine protease homologue cDNAs were isolated from Hyphantria cunea larvae induced immune response due to an injection of a microorganism through RT-PCR and cDNA library screening, and their characteristics were examined. The isolated cDNAs are composed 2.1 kb, 2.2 kb, and 2.5 kb nucleotide each, which encoded 388,390,580 amino acid residues, and were designated as HcPE-1, HcPE-2 and HcPE3, respectively. They were revealed as serine proteases or a serine protease homologue with the clip domain through a database search. The deduced amino acid sequence comparison showed high homology of $72-78\%$ among them. Six Cys residues of the N-terminal clip domain forming the disulfide bond, Cys residues of the catalytic domain, and Cys residues forming inter-bridge between clip domain and catalytic domain were also well preserved. Three amino acid residues, His, Asp, and Ser, within the active site were perfectly conserved in HcPE-2 and HcPE- 3, however, His was replaced with $Gln^{178}$ in HcPE-1. The Arg residues (HcPE-1, $Arg^{132}$; HcPE-2, $Arg^{134}$; HcPE-3, $Arg^{325}$) known as the activation sites by proteolytic cleavage were preserved well in all three types of protein. In case of HcPE-3, three continuous clip-like domains existed in the N terminal. As the result of phylogenetic analysis, three clip domain family of protein from H. cunea make groups with arthropod pro clotting enzyme precursor. Northern blot analysis showed all three genes were induced through an injection of Escherichia coli, but expression patterns were varied.
