FUNCTIONAL INTERACTIONS OF TRANSCRIPTION FACTOR HUMAN GA-BINDING PROTEIN SUBUNITS

The transcription factor human GA-binding protein (hGABP) is composed of two subunits, the Ets-related hGABP alpha, which binds to a specifi c DNA sequence, and either one of two hGABP alpha-associated subunits, hGABP beta or hGABP gamma, The DNA-binding protein hGABP alpha cannot affect transcription by itself, but can modify hGABP-dependent transc ription in vitro and in vivo in the presence of its associated subunit s. In this study, co-transfection assays showed that the ratio of hGAB P beta to hGABP gamma affected transcription from a promoter containin g hGABP binding sites. Biochemical analysis showed that they bind to h GABP alpha competitively, indicating that the ratio of hGABP beta to h GABP gamma is important for hGABP complex formation, Kinetic analysis of the protein-protein interaction using the surface plasmon resonance system showed that hGABP alpha binds to hGABP beta or hGABP gamma wit h similar equilibrium constants. Kinetic analysis of the DNA-hGABP int eraction showed that the binding of hGABP gamma to hGABP alpha stabili zed the interaction of hGABP alpha with its DNA binding site. In addit ion, the kinetic analysis revealed that this was due to a slower disso ciation of the protein complex from the DNA. These results suggest tha t hGABP alpha-associated subunits influence the DNA binding stability of hGABP alpha and regulate hGABP-mediated transcription by competing with each other.