Abstract: Bactericidal/permeability increasing protein（BPI）, an antimicrobial protein expressed in organism cells, shows particularantimicrobial activity against gram-negative bacteria. BPI contains two domains, N-terminal domain and C-terminal domain. The antibiotic andendotoxin-neutralizing functions of BPI are attributed to the N-terminal domain. The present study was performed with reference to the reportfor the recombinant DNA expression of human BPI. A cDNA fragment “BPI_Ntd” encoding the N-terminal active domain of BPI was clonedfrom the gill of channel catfish（Ictalurus punctatus）by RT-PCR and nested PCR. This fragment encodes a peptide consisting of 175 aminoacid residues, in which 63 residues can form a three-dimensional apolar lipid-binding pocket which is used to bind lipopolysaccharide（LPS）located in outer membrane of gram-negative bacteria. The comparison of the channel catfish BPI with the BPIs from other organisms showed that40 conserved amino acid residues appear at the N-terminal domain, and among them 9 highly conserved residues located in the LPS-bindingregion. The pET-32_a（+）and pET-28_a（+）with different characteristics were chosen as the prokaryotic expression vectors to constructthe prokaryotic expression system. “BPI_Ntd” fragment was inserted into these two plasmids respectively. The colony PCR, EcoR I and Hind IIIrestriction endonuclease digestion and DNA sequencing demonstrated that the “pET-32_a-BPI_Ntd” and “pET-28_a-BPI_Ntd” recombinant expressionplasmids were constructed successfully.

Key words: Channel catfish, BPI Domain, cDNA cloning, Prokaryotic expression