Participation of oligomerization through C-terminal D domain region of Sp1 in DNA binding

Transcription factor Sp1 is a Cys2His2-type zinc finger protein that specifically binds to GC-boxes on numerous viral and cellular genes. In this study, we prepared several Sp1 mutant peptides Sp1 (530-696) containing zinc finger region and the domain D, and Sp1 (530--623) containing only zinc finger region, and then investigated the participation of the C-terminal domain D of Sp1 for GC-box binding. Gel mobility shift assays demonstrate that Sp1 (530--696) evidently shows DNA-binding modes different from Spl (530--623) and that the Sp1 mutant containing the domain D self-interacts directly. Domain D may play an important role in the synergistic activation of Sp1 by the stacking of tetramers. A novel model for Sp1 oligomerization has also been proposed.