MOLECULAR CHARACTERIZATION OF THE B-BOX PROTEIN-PROTEIN INTERACTION MOTIF OF THE ETS-DOMAIN TRANSCRIPTION FACTOR ELK-1

The ternary complex factor (TCF) subfamily of ETS-domain transcription factors form ternary complexes with the serum response factor (SRF) a nd the c-fos SRE. Extracellular signals are relayed via MAP kinase sig nal transduction pathways through the TCF component of the ternary com plex. Protein-protein interactions between TCFs and SRF play an essent ial role in formation of this ternary complex. A 30 amino acid sequenc e encompassing the TCF B-box is sufficient to mediate interactions wit h SRF. In this study we have identified amino acids which are critical for this interaction and derived a molecular model of the SRF binding interface. Alanine scanning of the Elk-l B-box reveals five predomina ntly hydrophobic residues which are essential for binding to SRF and f or ternary complex formation in vitro and in vivo. These amino acids a re predicted to lie on one face of an alpha-helix, Peptides encompassi ng the B-box retain biological activity and have helix-forming propens ity. alpha-Helix and ternary complex formation is disrupted by the int roduction of helix-breaking proline residues. Our results are consiste nt with a model in which the Elk-l B-box forms an inducible alpha-heli x which, presents a hydrophobic face for interaction with SRF. We disc uss the wider applicability of our results to similar short protein-pr otein interaction moths found in other transcription factors.