USF2 FIP ASSOCIATES WITH THE B-ZIP TRANSCRIPTION FACTOR, C-MAF, VIA ITS BHLH DOMAIN AND INHIBITS C-MAF DNA-BINDING ACTIVITY/

In screening for proteins that interact with the basic zipper (bZip) t ranscription factor, c-Maf, we isolated USF2/FIP. USF2 is a member of the bHLH-Zip protein family, possessing a basic (b) DNA binding region , a helix-loop-helix (HLH) motif, and a leucine zipper (Zip) structure . Mutants of USF2 that lacked a Zip formed heterodimers with c-Maf, bu t did not homodimerize. Deletion of the USF2 basic region or mutation of its helices abrogated its binding to c-Maf, but had no effect on ho modimerization. A functional c-Maf bZip motif was necessary for both h omodimerization and heterodimerization with USF2. These data suggest a tetrameric configuration for Maf-USF2 complexes. In the presence of U SF2, the DNA binding activity of c-Maf was markedly reduced. Therefore , USF2 and c-Maf may interact to regulate gene expression. (C) 1997 Ac ademic Press.