Only two of the five zinc fingers of the eukaryotic transcriptional repressor PRDI-BF1 are required for sequence-specific DNA binding.

The eukaryotic transcriptional repressor PRDI-BF1 contains five zinc fingers of the C2H2 type, and the protein binds specifically to PRDI, a 14-bp regulatory element of the beta interferon gene promoter. We have investigated the amino acid sequence requirements for specific binding to PRDI and found that the five zinc fingers and a short stretch of amino acids N terminal to the first finger are necessary and sufficient for PRDI-specific binding. The contribution of individual zinc fingers to DNA binding was investigated by inserting them in various combinations into another zinc finger-containing DNA-binding protein whose own fingers had been removed. We found that insertion of PRDI-BF1 zinc fingers 1 and 2 confer PRDI-binding activity on the recipient protein. In contrast, the insertion of PRDI-BF1 zinc fingers 2 through 5, the insertion of zinc finger 1 or 2 alone, and the insertion of zinc fingers 1 and 2 in reverse order did not confer PRDI-binding activity. We conclude that the first two PRDI-BF1 zinc fingers together are sufficient for the sequence-specific recognition of PRDI.