INVOLVEMENT OF NEGATIVE COFACTOR NC2 IN ACTIVE REPRESSION BY ZINC FINGER-HOMEODOMAIN TRANSCRIPTION FACTOR AREB6

The transcription factor AREB6 contains a homeodomain Banked by two cl usters of Kruppel type C2H2 zinc fingers, AREB6 binds to the E-box con sensus sequence, CACCTGT, through either the N- or the C-terminal zinc finger cluster, To gain insights into the molecular mechanism by whic h AREB6 activates and represses gene expression, we analyzed the domai n structure of AREB6 in the context of a heterologous DNA-binding doma in by transient-transfection assays. The C-terminal region spanning am ino acids 1011 to 1124 was identified as a conventional acidic activat ion domain, The region containing amino acids 754 to 901, which was id entified as a repression domain, consists of 40% hydrophobic amino aci ds displaying no sequence similarities to other known repression domai ns, This region repressed transcription in vitro in a HeLa nuclear ext ract but not in reconstituted transcription systems consisting of tran scription factor IID (TFIID), TFIIB, TFIIE, TFIIH/F, and RNA polymeras e II. The addition of recombinant negative cofactor NC2 (NC2 alpha/DRA P1 and NC2 beta/Dr1) to the reconstituted transcription system restore d the activity of the AREB6 repression domain, We further demonstrated interactions between the AREB6 repression domain and NC2 alpha in yea st two-hybrid assay. Our findings suggest a mechanism of transcription al repression that is mediated by the general cofactor NC2.