CHICKEN INTERFERON CONSENSUS SEQUENCE-BINDING PROTEIN (ICSBP) AND INTERFERON REGULATORY FACTOR (IRF)-1 GENES REVEAL EVOLUTIONARY CONSERVATION IN THE IRF GENE FAMILY

Members of the IRF family mediate transcriptional responses to interfe rons (IFNs) and to virus infection. So far, proteins of this family ha ve been studied only among mammalian species, Here we report the isola tion of cDNA clones encoding two members of this family from chicken, interferon consensus sequence-binding protein (ICSBP) and IRF-1. The p redicted chicken ICSBP and IRF-1 proteins show high levels of sequence similarity to their corresponding human and mouse counterparts. Seque nce identities in the putative DNA-binding domains of chicken and huma n ICSBP and IRF-1 were 97% and 89%, respectively, whereas the C-termin al regions showed identities of 64% and 51%; sequence relationships wi th mouse ICSBP and IRF-1 are very similar. Chicken ICSBP was found to be expressed in several embryonic tissues, and both chicken IRF-1 and ICSBP were strongly induced in chicken fibroblasts by IFN treatment, s upporting the involvement of these factors in IFN regulated gene expre ssion. The presence of proteins homologous to mammalian IRF family mem bers, together with earlier observations on the occurrence of function ally homologous IFN-responsive elements in chicken and mammalian genes , highlights the conservation of transcriptional mechanisms in the IFN system, a finding that contrasts with the extensive sequence and func tional divergence of the IFNs.