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

Several alpha beta and gamma 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 alpha beta or gamma 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 alpha beta IFN (HLA-A3 and IFI-56K) or by gamma (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 post-translational modification(s) of the ISRE binding proteins responsible for altered binding properties.