Preferential binding sites for interferon regulatory factors 3 and 7 involved in interferon-A gene transcription

Transcription Factor Redundancy Ensures Induction of the Antiviral State

“…In a similar manner non-canonical ISREs mismatched at almost any position by a single base, demonstrate ISGF3-binding, presumably due to additional DNA:STAT1/2 contacts upstream of the core motif. In contrast, the IRF3 dimer demonstrates a more restricted DNA binding specificity, as it demands conservation for both of its ISRE half-sites (28,30). This difference is probably due to an extended loop in the DNA binding domain of IRF7 but not IRF3, providing more flexibility to engage in additional protein-protein interactions and direct contacts with the DNA (15).…”

“…The crystal structure of different IRFs bound to a DNA target sequence demonstrated that a dimeric IRF binds to two overlapping stretches of AANNGAAA, with the two IRF molecules occupying opposite sites of the DNA double helix, making minor groove contacts (AHA) with the first two A bases, and major groove contacts (AADH, ADAM, ADAM, ADAM) with the GAAA sequence (14,15,21,22). However, each family member performs its specific role in biological processes through distinct expression patterns and slightly different DNA binding specificities within the broad IRF consensus sequence (21,(23)(24)(25)(26)(27)(28)(29). While IRF9 is an integral component of ISGF3 and is essential in mediating IFN-induced transcriptional activity, two additional members, namely IRF3 and IRF7, function independently and are responsible for the induction of IFN (30,31).…”

Promoter Organization of the Interferon-A Genes Differentially Affects Virus-induced Expression and Responsiveness to TBK1 and IKK∈

“…Constructs carrying Ϫ78A/G (pIF4T-M78), Ϫ57G/C (pIF4T-M57), or both substitutions (pIF4T-M57/78) in the mouse IFN-A4 gene promoter were also described earlier (46). Promoters containing NN/TA substitutions in different GAAANN motifs were obtained by two-step PCR mutagenesis of the pIF4T plasmid.…”

“…The recombinant glutathione S-transferase proteins fused with the DNA-binding domain (DBD) of IRF-3 (residues 1-133) and IRF-7 (residues 1-150) were previously described (47). Binding reactions performed in the presence of 20 g/ml IRF-3(DBD), 400 g/ml IRF-7(DBD), or both recombinant proteins together for 30 min at room temperature and electrophoresis were described previously (46). The DNA-protein complexes were resolved on a 7% polyacrylamide (30:1) gel in 25 mM TEB, pH 8.3.…”

Regulation of the Transcriptional Activity of the IRF7 Promoter by a Pathway Independent of Interferon Signaling

“…IRF7 has a wider DNA-binding specificity (GAAWNYG-AAANY, W ϭ A or T, Y ϭ C or T) compared with IRF3 (GAAASSGAAANY, S ϭ G or C) (21). Studies on murine IFNA promoters showed that the core sequence GAAANN for IRF binding can be divided into four groups according to the identity of the NN: 1, the NC (N ϭ G, C, A, or T) and ST bases inducible by both IRF3 and IRF7; 2, the NG and CA preferentially responsive to IRF3; 3, the GAAAAT repeats responding only to IRF7; and 4, the DA (D ϭ T, A, or G) unresponsive to both factors (7,22). Interestingly, both the IRF7 ISRE and IRFE match the first group, which is inducible by both IRF3 and IRF7.…”