Analysis of the heteromeric DNA binding protein GABP has revealed the interaction of two distinct peptide sequence motifs normally associated with proteins located in different cellular compartments. The α subunit of GABP contains an 85-amino acid segment related to the Ets family of DNA binding proteins. The ETS domain of GABPα facilitates weak binding to DNA and, together with an adjacent segment of 37 amino acids, mediates stable interaction with GABPβ. The β subunit of GABP contains four imperfect repeats of a sequence present in several transmembrane proteins including the product of the Notch gene of Drosophila melanogaster. These amino-terminal repeats of GABPβ mediate stable interaction with GABPα and, when complexed with GABPα, directly contact DNA. These observations provide evidence for a distinct biochemical role for the 33-amino acid repeats, and suggest that they may serve as a module for the generation of specific dimerization interfaces.
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