Black Ben E, Brock Melissa A, Bédard Sabrina, Woods Virgil L, Cleveland Don W
Ludwig Institute for Cancer Research, University of California at San Diego, La Jolla, CA 92093, USA.
Proc Natl Acad Sci U S A. 2007 Mar 20;104(12):5008-13. doi: 10.1073/pnas.0700390104. Epub 2007 Mar 13.
Mammalian centromeres are defined epigenetically. Although the physical nature of the epigenetic mark is unknown, nucleosomes in which CENP-A replaces histone H3 are at the foundation of centromeric chromatin. Hydrogen/deuterium exchange MS is now used to show that assembly into nucleosomes imposes stringent conformational constraints, reducing solvent accessibility in almost all histone regions by >3 orders of magnitude. Despite this, nucleosomes assembled with CENP-A are substantially more conformationally rigid than those assembled with histone H3 independent of DNA template. Substitution of the CENP-A centromere targeting domain into histone H3 to convert it into a centromere-targeted histone that can functionally replace CENP-A in centromere maintenance generates the same more rigid nucleosome, as does CENP-A. Thus, the targeting information directing CENP-A deposition at the centromere produces a structurally distinct nucleosome, supporting a CENP-A-driven self-assembly mechanism that mediates maintenance of centromere identity.
哺乳动物的着丝粒是由表观遗传学定义的。尽管表观遗传标记的物理性质尚不清楚，但以CENP-A取代组蛋白H3的核小体是着丝粒染色质的基础。氢/氘交换质谱现在被用于表明组装成核小体会施加严格的构象限制，几乎使所有组蛋白区域的溶剂可及性降低超过3个数量级。尽管如此，与组蛋白H3组装的核小体相比，与CENP-A组装的核小体在构象上明显更刚性，且与DNA模板无关。将CENP-A着丝粒靶向结构域替换到组蛋白H3中，将其转化为一种可在着丝粒维持中功能性取代CENP-A的着丝粒靶向组蛋白，会产生与CENP-A相同的更刚性的核小体。因此，指导CENP-A在着丝粒处沉积的靶向信息产生了一种结构上不同的核小体，支持一种由CENP-A驱动的自组装机制，该机制介导着丝粒身份的维持。
