MOLECULAR CHARACTERIZATION AND TRANSCRIPTIONAL ANALYSIS OF INTERFERON-INDUCED 35 kDa PROTEIN HOMOLOG IDENTIFIED IN ROCK FISH Sebastes schlegelii

Interferon-induced protein-35 kDa (IFP35) is induced by Type II IFN (IFN-γ); it is a cytoplasmic protein that can be translocated to the nucleus via the stimulation of IFN. Here, we report the complete molecular characterization of the IFP35 cDNA sequence from the black rockfish (RfIFP35) in an effort to understand its role in the immune response. Based on full-length of RfIFP35 cDNA sequence, in silico characterization was conducted using bioinformatics tools and webservers. In addition, transcriptional analysis was conducted by using quantitative real time PCR.

The coding sequence of RfIFP35 encoded a putative peptide of 371 amino acids containing two characteristic Nmi/IFP 35 domains (NIDs), which are highly conserved among its counterparts. The protein showed a molecular mass of 42.2 kDa with a theoretical pI of 5.05 and was predicted to be unstable because of its high instability index (49.37). According to leucine zipper analysis, no leucine zipper motifs were identified in the RfIFP35 sequence, while this is a predominant characteristic feature of IFP35 in mammalian counterparts. RfIFP35 showed comparatively high aa sequence identity only with other fish homologs, but low identity to homologs in birds, reptiles, and mammals, indicating the uniqueness of the IFP35 gene in teleost. The folding index showed that RfIFP35 has the second highest percentage of disorder residues compared to mammals. Ubiquitous expression of RfIFP35 transcripts were determined by the basal tissue expression of black rockfish while highest level of expression was given by the blood tissue. The expression of RfIFP35 during immune challenge with poly I:C and lipopolysaccharide treatments affirms its putative importance in the first-line host defense system.