Specificities of protein-protein and protein-DNA interaction of GABPα and two newly defined ets-related proteins

The ets-related protein GABPα interacts with the four ankyrin-type (ANK) repeats of (GABPβ, to form a high-affinity DNA-binding complex that recognizes a site important for herpes simplex virus type I immediate early gene activation. To investigate the selectivity and specificity of the GABP complex, we have isolated two new ETS family members, termed ER81 and ER71. ER81 and GABPα were present in most tissues of adult mice, whereas ER71 was restricted to testis. We have compared the DNA-binding specificities of these proteins by binding site selection. GABPα, ER71, and ER81 recognized the common pentanucleotide DNA sequence 5'-CGGAA/T-3'. Although subtle differences were observed for nucleotide preferences flanking this pentanucleotide core, the overall similarity of the selected sequences was most striking. Given the observation that GABPα interaction with GABPβ requires its intact ETS domain, we further compared the ability of GABPβ to interact with other ETS proteins. GABPβ did not augment the DNA-binding activity of the highly similar ETS domains of ER81, ER71, or Ets-1. Moreover, probing of total tissue extracts with radiolabeled GABPβ demonstrated its exceedingly stringent specificity for GABPα. Given that the DNA-binding specificities of these ETS proteins are similar and that the protein-protein interactions between GABPβ and GABPα are highly specific, we conclude that the protein interactions determine the target site selection by GABPα.