Finnin M S, Hoffman D W, White S W
Department of Microbiology, Duke University Medical Center, Durham, NC 27710.
Proc Natl Acad Sci U S A. 1994 Nov 8;91(23):10972-6. doi: 10.1073/pnas.91.23.10972.
The bacteriophage T4 middle-mode transcription factor MotA consists of two domains of approximately equal size. The C-terminal domain has been shown to contain the DNA-binding elements of the molecule, and the N-terminal domain appears to interact with RNA polymerase. A 12.5-kDa fragment of the C-terminal domain (MotCF), comprising residues 105-211 of MotA, was found to be suitable for structural studies by NMR. The 1H and 15N assignments have been made for MotCF by using two-dimensional homonuclear and heteronuclear experiments. A secondary structure has been determined which consists of a six-stranded antiparallel beta-pleated sheet with three alpha-helical segments. The secondary structure of MotCF has a clear similarity to one half of the eukaryotic TATA-binding protein (TBP), which is an intramolecular dimer. Therefore, MotCF may be related to a monomeric ancestral protein of TBP. TBP binds its target DNA in the minor groove by specific interactions with hydrophobic and aromatic residues on the exposed sheet surface of the protein. Similar residues are also present on the beta-sheet surface of MotCF, suggesting that it too binds DNA in the minor groove.
噬菌体T4中模式转录因子MotA由两个大小近似相等的结构域组成。已证明C端结构域包含该分子的DNA结合元件，而N端结构域似乎与RNA聚合酶相互作用。发现C端结构域的一个12.5 kDa片段（MotCF），由MotA的105 - 211位残基组成，适用于通过核磁共振进行结构研究。通过二维同核和异核实验对MotCF进行了1H和15N归属。已确定其二级结构由一个具有三个α螺旋片段的六链反平行β折叠片组成。MotCF的二级结构与真核TATA结合蛋白（TBP）的一半有明显相似性，TBP是一种分子内二聚体。因此，MotCF可能与TBP的单体祖先蛋白有关。TBP通过与蛋白质暴露片层表面的疏水和芳香族残基的特异性相互作用在小沟中结合其靶DNA。MotCF的β折叠片表面也存在类似的残基，表明它也在小沟中结合DNA。
