ROLE OF IMPORTANT HYDROPHOBIC AMINO-ACIDS IN THE INTERACTION BETWEEN THE GLUCOCORTICOID RECEPTOR TAU-1-CORE ACTIVATION DOMAIN AND TARGET FACTORS

In this work, we determined how altered-function mutants affecting hyd rophobic residues within the tau 1-core activation domain of the human glucocorticoid receptor (GR) influence its physical interaction with different target proteins of the transcriptional machinery. Screening of putative target proteins showed that the tau 1-core can interact wi th the C-terminal part of the CREB-binding protein (CBP). In addition, the previously identified interactions of the tau 1-core with the TAT A-binding protein (TBP) and the Ada2 adaptor protein were localized to the C- and N-terminal regions of these proteins, respectively. A pane l of mutations within the tau 1-core that either decrease or increase activation potential was used to probe the interaction of the tau 1-co re domain with TBP, Ada2, and CBP. We found that the pattern of effect s caused by the mutations was similar for each of the interactions and that the effects on binding generally reflected effects on gene activ ation potential. Thus, the predominant effect of the mutations appears to influence a property of the tau 1-core that is common to all three interactions, rather than properties that are differentially required by each of the target factor interactions, individually, Such a prope rty could be the ability of the domain to adopt a folded conformation that is generally necessary for interaction with target factors. We ha ve also shown that TBP, Ada2, and CBP can interact with both the tau 1 -core and the GR ligand-binding domain, offering a possible mechanism for synergistic interaction between the tau 1-core and other receptor activation domains. However, other target proteins (e.g., RIP140, and SRC-1), which interact with the GR C terminus, did not show significan t interactions with the tau 1-core under our conditions.