Crystal structure of Negative Cofactor 2 recognizing the TBP-DNA transcription complex

The X-ray structure of a ternary complex of Negative Cofactor 2 (NC2), the TATA box binding protein (TBP), and DNA has been determined at 2.6 Angstrom resolution. The N termini of NC2 alpha and beta resemble histones H2A and H2B, respectively, and form a heterodimer that binds to the bent DNA double helix on the underside of the preformed TBP-DNA complex via electrostatic interactions. NC2 beta contributes to inhibition of TATA-dependent transcri ption through interactions of its C-terminal or helix with a conserved hydr ophobic feature on the upper surface of TBP, which in turn positions the pe nultimate a helix of NC2 beta to block recognition of the TBP-DNA complex b y transcription factor IIB. Further regulatory implications of the NC2 hete rodimer structure are discussed.