DNA-protein interactions at the interferon-responsive promoter: evidences for an involvement of phosphorylation

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Abstract
Several αβ and γ interferons (IFN) induced genes are regulated transcriptionally via a 29 bp cis acting regulatory element (ICS, Interferon Consensus Sequence). The ICS binding capacity of HeLa cell nuclear extracts was strictly dependent on the presence of nucleoside triphosphate and Mg2+. It increased upon αβ or γ IFN treatment of the cells. Three 50 mer synthetic oligonucleotides containing the ICS or putative ISRE (Interferon Stimulatable Response Element), representing portions of genes inducible by αβ IFN (HLA-A3 and IFI-56K) or by γ (HLA-DR) were used as probes to titrate nuclear factors interacting with the ICS. All three probes were retarded in a mobility shift assay in two bands. Phosphorylation conditions were crucial for demonstrating their existence and/or their relative amounts. A factor whose activity and/or amount was modulated upon IFN treatment, appeared to be involved in phosphorylation dependent posttransiational modification(s) of the ISRE binding proteins responsible for altered binding properties.