Li G, Lim K C, Engel J D, Bungert J
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60208-3500, USA.
Genes Cells. 1998 Jul;3(7):415-29. doi: 10.1046/j.1365-2443.1998.00200.x.
The human beta-globin locus control region (LCR) is composed of five DNase I hypersensitive (HS) sites located 5' to the multiple genes it regulates. The LCR has been shown to comprise, among other essential properties, an activity that is required for generating a chromatin structure which renders the entire beta-globin gene locus accessible to exogenous nucleases. This nuclease-sensitive state is generally believed to be reflective of the chromatin environment that is permissive for transcriptional activation of the globin genes.
Here we show, in mice bearing intact YAC transgenes that encompass the whole human beta-globin locus, that the deletion of individual core LCR HS sites negatively affects the ability of the LCR to confer this open chromatin conformation throughout the locus, and when analysed in concert with the effect that these same mutations have on transcription, the data show that the chromatin opening activity is a necessary, but not sufficient, prerequisite for globin gene expression. The results also show that after deletion of individual hypersensitive sites, the mutated LCR is no longer able to provide an accessible chromatin environment that is independent from the site of YAC transgene integration.
These experiments provide further evidence for the hypothesis that the HS sites must act cooperatively to fulfil the multiple functions that are attributable to the LCR.
人类β-珠蛋白基因座控制区（LCR）由五个位于其调控的多个基因5'端的DNA酶I超敏（HS）位点组成。LCR已被证明除其他基本特性外，还具有一种活性，这种活性对于产生一种染色质结构是必需的，该结构使整个β-珠蛋白基因座对外源核酸酶可及。这种核酸酶敏感状态通常被认为反映了有利于珠蛋白基因转录激活的染色质环境。
在这里，我们在携带包含整个人类β-珠蛋白基因座的完整酵母人工染色体（YAC）转基因的小鼠中表明，单个核心LCR HS位点的缺失会对LCR在整个基因座赋予这种开放染色质构象的能力产生负面影响，并且当与这些相同突变对转录的影响一起分析时，数据表明染色质开放活性是珠蛋白基因表达的必要但非充分前提条件。结果还表明，在单个超敏位点缺失后，突变的LCR不再能够提供独立于YAC转基因整合位点的可及染色质环境。
这些实验为以下假设提供了进一步的证据，即HS位点必须协同作用以履行归因于LCR的多种功能。
