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Mol. Cell. Biol., 11 1996, 6083-6095, Vol 16, No. 11
T Oyake, K Itoh, H Motohashi, N Hayashi, H Hoshino, M Nishizawa, M Yamamoto and K Igarashi
Members of the small Maf family (MafK, MafF, and MafG) are basic region
leucine zipper (bZip) proteins that can function as transcriptional
activators or repressors. The dimer compositions of their DNA binding forms
determine whether the small Maf family proteins activate or repress
transcription. Using a yeast two-hybrid screen with a GAL4-MafK fusion
protein, we have identified two novel bZip transcription factors, Bach1 and
Bach2, as heterodimerization partners of MafK. In addition to a
Cap'n'collar-type bZip domain, these Bach proteins possess a BTB domain
which is a protein interaction motif; Bach1 and Bach2 show significant
similarity to each other in these regions but are otherwise divergent.
Whereas expression of Bach1 appears ubiquitous, that of Bach2 is restricted
to monocytes and neuronal cells. Bach proteins bind in vitro to NF-E2
binding sites, recognition elements for the hematopoietic transcription
factor NF-E2, by forming heterodimers with MafK. Furthermore, a DNA binding
complex that contained MafK as well as Bach2 or a protein related closely
to Bach2 was found to be present in mouse brain cells. Bach1 and Bach2
function as transcription repressors in transfection assays using
fibroblast cells, but they function as a transcriptional activator and
repressor, respectively, in cultured erythroid cells. The results suggest
that members of the Bach family play important roles in coordinating
transcription activation and repression by MafK.
Copyright © 1996, American Society for Microbiology
Bach proteins belong to a novel family of BTB-basic leucine zipper transcription factors that interact with MafK and regulate transcription through the NF-E2 site
Department of Biochemistry, Tohoku University School of Medicine, Sendai, Japan.
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