MOLECULAR-BASIS OF COOPERATIVE DNA BENDING AND ORIENTED HETERODIMER BINDING IN THE NFAT1-FOS-JUN-ARRE2 COMPLEX

Cooperative DNA binding by transcription factors that bind to separate recognition sites is likely to require bending of intervening sequenc es and the appropriate orientation of transcription factor binding. We investigated DNA bending in complexes formed by the basic region-leuc ine zipper domains of Fos and Jun with the DNA binding region of nucle ar factor of activated T cells 1 (NFAT1) at composite regulatory eleme nts using gel electrophoretic phasing analysis. The NFAT1-Fos-Jun comp lex induced a bend at the ARRE2 site that was distinct from the sum of the bends induced by NFAT1 and Fos-Jun separately. We designate this difference DNA bending cooperativity. The bending cooperativity was di rected toward the interaction interface between Fos-Jun and NFAT1. We also examined the influence of NFAT1 on the orientation of Fos-Jun het erodimer binding using a novel fluorescence resonance energy transfer assay, The interaction with NFAT1 could reverse the orientation of Fos -Jun heterodimer binding to the ARRE2 site. The principal determinants of both cooperative DNA bending and oriented heterodimer binding were localized to three amino acid residues at the amino-terminal ends of the leucine zippers of Fos and Jun. Consequently, interactions between transcription factors fan remodel promoters by altering DNA bending a nd the orientation of heterodimer binding.