Structure of NFAT1 bound as a dimer to the HIV-1 LTR κB element

DNA binding by NFAT1 as a dimer has been implicated in the activation of host and viral genes. Here we report a crystal structure of NFAT1 bound cooperatively as a dimer to the highly conserved B site from the human immunodeficiency virus 1 ( HIV-1) long terminal repeat (LTR). This structure reveals a new mode of dimerization and protein-DNA recognition by the Rel homology region (RHR) of NFAT1. The two NFAT1 monomers form a complete circle around the B DNA through protein-protein interactions mediated by both their N- and C-terminal subdomains. The major dimer interface, formed by the C-terminal domain, is asymmetric and substantially different from the symmetric dimer interface seen in other Rel family proteins. Comparison to other NFAT structures, including NFAT5 and the NFAT1 Fos-JunARRE2 complex, reveals that NFAT1 adopts different conformations and its protein surfaces mediate distinct protein-protein interactions in the context of different DNA sites.