Dickinson L A, Dickinson C D, Kohwi-Shigematsu T
Burnham Institute, La Jolla Cancer Research Center, La Jolla, California 92037, USA.
J Biol Chem. 1997 Apr 25;272(17):11463-70. doi: 10.1074/jbc.272.17.11463.
SATB1 is a cell type-specific nuclear matrix attachment region (MAR) DNA-binding protein, predominantly expressed in thymocytes. We identified an atypical homeodomain and two Cut-like repeats in SATB1, in addition to the known MAR-binding domain. The isolated MAR-binding domain recognizes a certain DNA sequence context within MARs that is highly potentiated for base unpairing. Unlike the MAR-binding domain, the homeodomain when isolated binds poorly and with low specificity to DNA. However, the combined action of the MAR-binding domain and the homeodomain allows SATB1 to specifically recognize the core unwinding element within the base-unpairing region. The core unwinding element is critical for MAR structure, since point mutations within this core abolish the unwinding propensity of the MAR. The contribution of the homeodomain is abolished by alanine substitutions of arginine 3 and arginine 5 in the N-terminal arm of the homeodomain. Site-directed mutagenesis of the core unwinding element in the 3' MAR of the immunoglobulin heavy chain gene enhancer revealed the sequence 5'-(C/A)TAATA-3' to be essential for the increase in affinity mediated by the homeodomain. SATB1 may regulate T-cell development and function at the level of higher order chromatin structure through the critical DNA structural elements within MARs.
SATB1是一种细胞类型特异性的核基质附着区域（MAR）DNA结合蛋白，主要在胸腺细胞中表达。除了已知的MAR结合结构域外，我们在SATB1中鉴定出一个非典型的同源异型结构域和两个Cut样重复序列。分离出的MAR结合结构域识别MAR内特定的DNA序列上下文，该上下文对碱基解配对具有高度增强作用。与MAR结合结构域不同，分离出的同源异型结构域与DNA的结合能力差且特异性低。然而，MAR结合结构域和同源异型结构域的联合作用使SATB1能够特异性识别碱基解配对区域内的核心解旋元件。核心解旋元件对MAR结构至关重要，因为该核心内的点突变会消除MAR的解旋倾向。同源异型结构域的贡献通过同源异型结构域N端臂中精氨酸3和精氨酸5的丙氨酸替代而消除。免疫球蛋白重链基因增强子3'MAR中核心解旋元件的定点诱变表明，序列5'-(C/A)TAATA-3'对于同源异型结构域介导的亲和力增加至关重要。SATB1可能通过MAR内的关键DNA结构元件在高阶染色质结构水平上调节T细胞的发育和功能。
