The present work demonstrates that the ISAV proteins s7ORF1
and s8ORF2 inhibit IRF- mediated activation of the Atlantic salmon
IFNa1 promoter. s7ORF1 most strongly inhibited activation of the
promoter by IRF3 and IRF7B, while s8ORF2 most strongly inhibited
activation of the promoter by IRF1 and IRF3. Interactions between
the ISAV proteins and the IRFs were supported by immunoprecipitation
studies, which showed immunoprecipitation bands for all
four IRFs when co-transfected with FLAG-tagged s7ORF1 or
s8ORF2. This suggests that the virus proteins interact with a peptide
epitope that is common for the four IRFs. The candidate region
is the DNA-binding region since the four IRFs shows a high level of