Crichlow Gregg V, Zhou Hongwen, Hsiao Hsin-hao, Frederick Kendra B, Debrosse Maxime, Yang Yuande, Folta-Stogniew Ewa J, Chung Hye-Jung, Fan Chengpeng, De la Cruz Enrique M, Levens David, Lolis Elias, Braddock Demetrios
Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06510, USA.
EMBO J. 2008 Jan 9;27(1):277-89. doi: 10.1038/sj.emboj.7601936. Epub 2007 Dec 6.
c-myc is essential for cell homeostasis and growth but lethal if improperly regulated. Transcription of this oncogene is governed by the counterbalancing forces of two proteins on TFIIH--the FUSE binding protein (FBP) and the FBP-interacting repressor (FIR). FBP and FIR recognize single-stranded DNA upstream of the P1 promoter, known as FUSE, and influence transcription by oppositely regulating TFIIH at the promoter site. Size exclusion chromatography coupled with light scattering reveals that an FIR dimer binds one molecule of single-stranded DNA. The crystal structure confirms that FIR binds FUSE as a dimer, and only the N-terminal RRM domain participates in nucleic acid recognition. Site-directed mutations of conserved residues in the first RRM domain reduce FIR's affinity for FUSE, while analogous mutations in the second RRM domain either destabilize the protein or have no effect on DNA binding. Oppositely oriented DNA on parallel binding sites of the FIR dimer results in spooling of a single strand of bound DNA, and suggests a mechanism for c-myc transcriptional control.
c-myc 对于细胞稳态和生长至关重要，但如果调控不当则具有致死性。该癌基因的转录受两种蛋白质对 TFIIH 的平衡作用调控，这两种蛋白质分别是 FUSE 结合蛋白（FBP）和 FBP 相互作用阻遏物（FIR）。FBP 和 FIR 识别 P1 启动子上游的单链 DNA（称为 FUSE），并通过在启动子位点对 TFIIH 进行相反方向的调控来影响转录。尺寸排阻色谱结合光散射显示，一个 FIR 二聚体结合一分子单链 DNA。晶体结构证实 FIR 以二聚体形式结合 FUSE，并且只有 N 端的 RRM 结构域参与核酸识别。第一个 RRM 结构域中保守残基的定点突变降低了 FIR 对 FUSE 的亲和力，而第二个 RRM 结构域中的类似突变要么使蛋白质不稳定，要么对 DNA 结合没有影响。FIR 二聚体平行结合位点上相反方向的 DNA 导致一条结合的单链 DNA 形成线轴状，这提示了 c-myc 转录调控的一种机制。
