Molecular cloning of a novel interferon regulatory factor in Japanese flounder, Paralichthys olivaceus.

A complementary DNA library was constructed in lambda ZAP II using messenger RNA from the leukocytes of some heterocloned Japanese flounder, Paralichthys olivaceus, that had been artificially infected with Hirame rhabdovirus (HRV). A cloned flounder interferon regulatory factor (designated fIRF) cDNA was found to be 1746 bp in length, with an open reading frame of 297 amino acids. The overall amino acid sequence of fIRF had approximately 40% identity with the previously reported avian and mammalian IRF-1s and IRF-2s. The fIRF sequence was most similar to that recorded for the chicken IRF-1. Amino acid sequence identities between the DNA-binding domain of the fIRF and that of both chicken IRF-1 and chicken IRF-2 were 72.3%. The DNA-binding domain of fIRF contained the repeated tryptophan motif that is characteristic of members of the IRF family. The mRNA of fIRF was detected in various tissues by reverse transcription-polymerase chain reaction (RT-PCR). The fIRF was transcribed mainly in the intestine, ovary, muscle, liver, heart and spleen, while it was minimally transcribed in the brain and kidney. When Japanese flounder were injected with HRV, the relative expression of fIRF mRNA was found to increase and peak 3 days after injection. The quantities of the fIRF mRNA increased to levels that were 7.5-fold higher than those of noninjected fish. In addition, when Japanese flounder were injected with Edwardsiella tarda, the expression of fIRF mRNA showed increases 2, 3, and 4 days after injection. The quantities of the fIRF mRNA on those days represented approximately 6-, 15-, and 14-fold increases, respectively, over the levels in noninjected fish.