Identification and expression analysis of an interferon stimulated gene 15 (ISG15) from black rockfish, Sebastes schlegeli

The interferon stimulated gene 15 (ISG15) is strongly induced in many cell types by IFNs, viral infection and double-stranded RNA (poly I:C). The ISG15 homolog cDNA was isolated from the black rockfish poly I:C stimulated leukocyte cDNA library. The black rockfish ISG15 homolog was found to consist of 1070 bp encoding 160 amino acid residues. Compared with other known ISG15 peptide sequences, the most conserved regions of the black rockfish ISG15 peptide were found to be the tandem ubiquitin-like domains and a C-terminal LRLRGG conjugating motif, characteristic of mammalian and non-mammalian ISG15 proteins. A phylogenetic analysis based on the deduced amino acid sequence revealed a homologous relationship between the ISG15 sequence of black rockfish and that of Atlantic salmon, Atlantic cod, crucian carp and rainbow trout. The expression of the black rockfish ISG15 molecule was induced in the peripheral blood leukocytes (PBLs) from 1 to 12 h following poly I:C stimulation, with a peak at 6 h post-stimulation. The black rockfish gene was predominantly expressed in the PBLs and the spleen.