Proteinase inhibitors play important roles in host defence systems involving 
blood coagulation and pathogen digestion. We isolated and characterized a cDNA 
clone for a Kazal-type proteinase inhibitor (KPI) from a hemocyte cDNA library 
of the oriental white shrimp Fenneropenaeus chinensis. The KPI gene consists of 
three exons and two introns. KPI cDNA contains an open reading frame of 396 bp, 
a polyadenylation signal sequence AATAAA, and a poly (A) tail. KPI cDNA encodes 
a polypeptide of 131 amino acids with a putative signal peptide of 21 amino 
acids. The deduced amino acid sequence of KPI contains two homologous Kazal 
domains, each with six conserved cysteine residues. The mRNA of KPI is expressed 
in the hemocytes of healthy shrimp, and the higher expression of KPI transcript 
is observed in shrimp infected with the white spot syndrome virus (WSSV), 
suggesting a potential role for KPI in host defence mechanisms.