REX-1, A GENE ENCODING A TRANSCRIPTION FACTOR EXPRESSED IN RBE EARLY EMBRYO, IS REGULATED VIA OCT-3 4 AND OCT-6 BINDING TO AN OCTAMER SITE AND A NOVEL PROTEIN, ROX-1, BINDING TO AN ADJACENT SITE/

The Rex-1 (Zfp-42) gene, which encodes an acidic zinc finger protein, is expressed at high levels in embryonic stern (ES) and F9 teratocarci noma cells, Prior analysis identified an octamer motif in the Rex-1 pr omoter which is required for promoter activity in undifferentiated F9 cells and is involved in retinoic acid (RA)-associated reduction in ex pression. We show here that the Oct-3/4 transcription factor, but not Oct-1, can either activate or repress the Rex-1 promoter, depending on the cellular environment, Rex-1 repression is enhanced by EIA. The pr otein domain required for Oct-3/4 activation was mapped to amino acids 1 to 35, whereas the domain required for Oct-3/4 repression was mappe d to amino acids 61 to 126, suggesting that the molecular mechanisms u nderlying transcriptional activation and repression differ. Like Oct-3 /4, Oct-6 can also lower the expression of the Rex-1 promoter via the octamer site, and the amino-terminal portion of Oct-6 mediates this re pression, In addition to the octamer motif, a novel positive regulator y element, located immediately 5' of the octamer motif, was identified in the Rex-1 promoter, Mutations in this element greatly reduce Rex-1 promoter activity in F9 cells, High levels of a binding protein(s), d esignated Rox-1, recognize this novel DNA element in F9 cells, and thi s binding activity is reduced following RA treatment. Taken together, these results indicate that the Rex-1 promoter is regulated by specifi c octamer family members in early embryonic cells and that a novel ele ment also contributes to Rex-1 expression.