Cloning and phylogenetic analysis of the interleukin-18 gene in gushi duck

A pair of primers was designed according to duck IL-18 gene sequences in GenBank.Duck IL-18 gene was amplified by RT-PCR from total RNA extracted from gushi duck splenocyte and the PCR product was cloned and sequenced.The result showed that the duck IL-18 gene is 603 bp in length encoding 200 amino acids.The gene is highly conserved and shared 98.8 %-99.8 % nucleotide homology and 97.5 %-99.5 % amino acid homology with other duck IL-18 genes(accession No.AF336122 and DQ490137).Thje gene contains a putative caspase-1 cleavage site of IL-1beta-converting enzyme(ICE) at aspartic acid 30 of the primary translation product and IL-1 signature-like sequences similar to those identified in human and others mammals IL-18,indicating that a mature DuIL-18 might comprise 170 amino acids.Phylogenetic tree analysis indicated that the IL-18 sequence variation was related to genus,the nearer relationship,the higher homology.