The promoter of mouse transcription repressor bach1 is regulated by Sp1 and trans-activated by Bach1

The Maf recognition element (MARE) is regulated by both activators and repr essors. Bach1 and Bach2 repress MARE-dependent transcription by forming het erodimers with Maf-related oncoproteins. In order to gain an understanding of the regulation of bach1 gene expression, we analyzed the structure of th e mouse bach1 gene. Comparison of the exon-intron structure of the bach1 ge ne with those of other NF-E2-related genes indicated that bach1 and bach2 c onstitute an evolutionarily distinct subfamily among bZip factors. The bach 1 promoter region contains two GC boxes that are important for its basal ac tivity and are bound by Sp1 in K562 cell extracts. In addition, we found an evolutionarily conserved MARE-like element located downstream of the trans cription initiation site. Deletion of this element resulted in a higher pro moter activity in K562 cells. Bach1 trans-activated its own promoter depend ing on the presence of the MARE-like element in co-transfection assays. How ever, Bach1 did not bind to the MARE-like element in electrophoretic mobili ty shift assays (EMSA). These results suggest that Bach1 activates its own promoter indirectly by inhibiting the putative repressor. Such a positive f eedback regulation by the repressor Bach1 may play an important role in mai ntaining the expression of Bach1 while consolidating repression of other ge nes with MARE.