THE REDOX AND DNA-REPAIR ACTIVITIES OF REF-1 ARE ENCODED BY NONOVERLAPPING DOMAINS

The DNA binding activity of transcription factor AP-1 is regulated in vitro by a posttranslational mechanism involving reduction/oxidation ( redox). Redox regulation is mediated by a conserved cysteine residue i n the DNA-binding domain of Fos and Jun. Previously, we demonstrated t hat a DNA repair protein, Ref-1, could stimulate the DNA binding activ ity of Fos-Jun dimers by reducing this cysteine residue. To examine th e relationship between the redox and repair functions of Ref-1, we gen erated a series of deletion mutants. Analysis of the truncated protein s in vitro revealed that the redox and repair activities are encoded b y distinct regions of Ref-1. Sequences in the N-terminal domain of Ref -1 that are not present in functionally related proteins from other or ganisms are required for the redox activity, whereas the DNA repair ac tivity requires conserved C-terminal sequences. Chemical alkylation or oxidation of cysteine sulfhydryls inhibits the redox activity of Ref- 1 without affecting its DNA repair activity. Crosslinking studies sugg est that a direct cysteine-mediated interaction occurs between Ref-1 a nd Jun.