O'Neill D, Yang J, Erdjument-Bromage H, Bornschlegel K, Tempst P, Bank A
Department of Pathology, Columbia University College of Physicians and Surgeons, 701 West 168th Street, New York, NY 10032, USA.
Proc Natl Acad Sci U S A. 1999 Jan 19;96(2):349-54. doi: 10.1073/pnas.96.2.349.
SWI/SNF complexes in yeast and higher eukaryotes are thought to facilitate gene activation and transcription factor binding by disrupting repressive chromatin structures. Little is known, however, about how these complexes target specific genes for activation. We now have purified a specialized SWI/SNF-related complex (PYR complex) from murine erythroleukemia (MEL) cell nuclear extract that binds pyrimidine-rich elements at the human and murine beta-globin loci. PYR complex DNA-binding activity is restricted to definitive hematopoietic cells and is both DNA sequence- and length-dependent. Mass spectrometric identification of purified peptides and antibody supershift assays indicate that PYR complex contains at least four known mammalian SWI/SNF subunits: BAF57, INI1, BAF60a, and BAF170. PYR complex broadly footprints a 250-bp pyrimidine-rich element between the human fetal and adult beta-globin genes. A short intergenic deletion that removes this element from a human globin locus cosmid construct results in delayed human fetal-to-adult globin gene switching in transgenic mice. Taken together, the data suggest that PYR complex may act through this intergenic element to facilitate human fetal-to-adult globin gene switching, presumably by opening the locus in the region of the adult genes to permit the binding of beta-globin transcriptional activators.
酵母和高等真核生物中的SWI/SNF复合物被认为通过破坏抑制性染色质结构来促进基因激活和转录因子结合。然而，对于这些复合物如何靶向特定基因进行激活却知之甚少。我们现在从鼠红细胞白血病（MEL）细胞核提取物中纯化出一种特殊的与SWI/SNF相关的复合物（PYR复合物），它能与人及鼠β-珠蛋白基因座上富含嘧啶的元件结合。PYR复合物的DNA结合活性仅限于成熟造血细胞，且依赖于DNA序列和长度。对纯化肽段的质谱鉴定和抗体超迁移分析表明，PYR复合物至少包含四种已知的哺乳动物SWI/SNF亚基：BAF57、INI1、BAF60a和BAF170。PYR复合物广泛覆盖人胎儿和成人β-珠蛋白基因之间一个250bp富含嘧啶的元件。从人珠蛋白基因座黏粒构建体中删除该元件的一个短基因间缺失导致转基因小鼠中胎儿型到成人型珠蛋白基因转换延迟。综上所述，数据表明PYR复合物可能通过这个基因间元件发挥作用，以促进人胎儿型到成人型珠蛋白基因转换，推测是通过打开成人基因区域的基因座，以允许β-珠蛋白转录激活因子的结合。
