Functional domains of interferon regulatory factor I (IRF-1)

Abstract

Interferon (IFN) regulatory factors (IRFs) are a family of transcription factors among which are IRF-1, IRF-2, and IFN consensus sequence binding protein (ICSBP). These factors share sequence homology in the N-terminal DNA-binding domain. IRF-1 and IRF-2 are further related and have additional homologous sequences within their C-termini. Whereas IRF-2 and ICSBP are identified as transcriptional repressors, IRF-1 is an activator. In the present work, the identification of functional domains in murine IRF-1 with regard to DNA-binding, nuclear translocation, heterodimerization with ICSBP and transcriptional activation are demonstrated. The minimal DNA-binding domain requires the N-terminal 124 amino acids plus an arbitrary C-terminal extension. By using mutants of IRF-1 fusion proteins with green fluorescent protein and monitoring their distribution in living cells, a nuclear location signal (NLS) was identified and found to be sufficient for nuclear translocation. Heterodimerization was confirmed by a two-hybrid system adapted to mammalian cells. The heterodimerization domain in IRF-1 was defined by studies in vitro and was shown to be homologous with a sequence in IRF-2, suggesting that IRF-2 also heterodimerizes with ICSBP through this sequence. An acidic domain in IRF-1 was found to be required and to be sufficient for transactivation. Epitope mapping of IRF-1 showed that regions within the NLS, the heterodimerization domain and the transcriptional activation domain are exposed for possible contacts with interacting proteins.

An IFN-γ-Inducible Transcription Factor, IFN Consensus Sequence Binding Protein (ICSBP), Stimulates IL-12 p40 Expression in Macrophages

“…However, despite the inability to stimulate promoter activity on its own, IRF-1, when cotransfected with ICSBP, gave cooperative activation of IL-12 p40 promoter activity (Fig. 5), probably by direct interaction with ICSBP through the heterodimerization domain (45). Our data indicate that while ICSBP is an obligatory activator, IRF-1 plays an auxiliary role in IL-12 p40 transcription.…”

Bipartite Nuclear Localization Signal Controls Nuclear Import and DNA-Binding Activity of IFN Regulatory Factor 3

“…The IRF family contains nine mammalian members (IRF1, IRF2, IRF3, IRF4, IRF5, IRF6, IRF7, IRF8, and IRF9), which are most conserved in their DBD. IRF1 and IRF2, which are closely related to each other, contain a conserved NLS located immediately C-terminal to the DBD, involving aa 120-138 (33). IRF4, IRF8, and IRF9 are highly conserved with each other and use the homologous NLS (aa 66-85) to direct their accumulation in the nucleus (34).…”

Gene structure and transcription of IRF-2 in the mandarin fish Siniperca chuatsi with the finding of alternative transcripts and microsatellite in the coding region

“…Structurally, all members of the IRF family share homology in their first 115 amino acids (aa), encompassing the DNA binding domain that contains a characteristic repeat of tryptophans; the carboxyl-terminal regions of these proteins are more diverse. All IRFs, except IRF-1 and IRF-2, have an IRF association domain (IAD) that is responsible for interaction with other family members or transcription factors, whereas IRF-1 and IRF-2 contain another association domain (IAD2) (aa 210-265 in human IRF-2) that is essential for their interaction with IRF-8 (Schaper et al 1998;Meraro et al 1999). The IRF-2 also contains the acidic region (aa 182-218) functioned as a transactivating domain (Jesse et al 1998).…”