Binding of nuclear factors to the 5'-interferon consensus sequence of the HLA-A2 class I gene

To investigate the regulatory role of the conserved interferon consensus sequence (ICS) found in the 5' flanking region of HLA class I genes, we studied the binding of nuclear proteins to the ICS of HLA-A2 gene (ICS-A2) by the gel shift assay. Nuclear extracts from several human cell lines expressing different levels of surface class I molecules reveal an ICS-A2-protein complex of similar mobility, the amount of which varies in a cell type-dependent manner. In some cell lines, interferon-gamma treatment decreased the level of this complex. The overlapping enhancer A element also competes for the formation of this ICS-A2-protein complex. Footprinting and methylation interference analyses demonstrate that nuclear protein(s) protect specific sequences within the ICS-A2 element, suggesting that these protein(s) may represent interferon-sensitive transcription factors.