SP3 REPRESSES TRANSCRIPTION WHEN TETHERED TO PROMOTER DNA OR TARGETEDTO PROMOTER PROXIMAL RNA

Sp3 is a member of the Sp family of transcription factors, and it bind s to the GC box with an affinity and specificity comparable with that of Spl. Previous studies have shown that Sp3 repressed Spl-mediated tr anscriptional activation, suggesting that Sp3 is an inhibitory member of the Sp family. The experiments described here demonstrate that Sp3 contains a portable repression domain that can function independently from the zinc finger DNA binding domain. We found that the amino-termi nal region of Sp3 tethered to a promoter DNA by connecting to a hetero logous DNA-binding protein domain represses transcriptional activation by different positive regulators. Moreover, we determined that Sp3 ta rgeted to a promoter-proximal RNA sequence acts as a transcriptional r epressor. Taken together, our results suggest that Sp3 functions as a repressor by protein-protein interaction with components of the genera l transcription complex.