Vanathi Perumal, Mishra Anurag Kumar, Bhargava Purnima
Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India.
J Biosci. 2003 Jun;28(4):413-21. doi: 10.1007/BF02705116.
Dimerization is proposed to be a regulatory mechanism for TATA-binding protein (TBP) activity both in vitro and in vivo. The reversible dimer-monomer transition of TBP is influenced by the buffer conditions in vitro. Using in vitro chemical cross-linking, we found yeast TBP (yTBP) to be largely monomeric in the presence of the divalent cation Mg2+, even at high salt concentrations. Apparent molecular mass of yTBP at high salt with Mg2+, run through a gel filtration column, was close to that of monomeric yTBP. Lowering the monovalent ionic concentration in the absence of Mg2+, resulted in dimerization of TBP. Effect of Mg2+ was seen at two different levels: at higher TBP concentrations, it suppressed the TBP dimerization and at lower TBP levels, it helped keep TBP monomers in active conformation (competent for binding TATA box), resulting in enhanced TBP-TATA complex formation in the presence of increasing Mg2+. At both the levels, activity of the full-length TBP in the presence of Mg2+ was like that reported for the truncated C-terminal domain of TBP from which the N-terminus is removed. Therefore for full-length TBP, intra-molecular interactions can regulate its activity via a similar mechanism.
二聚化被认为是一种在体外和体内调节TATA结合蛋白（TBP）活性的机制。TBP可逆的二聚体-单体转变受体外缓冲条件的影响。通过体外化学交联，我们发现酵母TBP（yTBP）在二价阳离子Mg2+存在的情况下，即使在高盐浓度下也主要以单体形式存在。通过凝胶过滤柱测定，在高盐和Mg2+存在的情况下，yTBP的表观分子量接近单体yTBP的分子量。在没有Mg2+的情况下降低单价离子浓度会导致TBP二聚化。Mg2+的作用体现在两个不同层面：在较高的TBP浓度下，它抑制TBP二聚化；在较低的TBP水平下，它有助于使TBP单体保持活性构象（能够结合TATA框），从而在Mg2+浓度增加时增强TBP-TATA复合物的形成。在这两个层面上，Mg2+存在时全长TBP的活性与报道的去除N端的TBP截短C端结构域的活性相似。因此，对于全长TBP，分子内相互作用可以通过类似的机制调节其活性。
