Baniahmad A, Muller M, Steiner C, Renkawitz R
Max-Planck-Institut für Biochemie, Genzentrum, Martinsried, FRG.
EMBO J. 1987 Aug;6(8):2297-303. doi: 10.1002/j.1460-2075.1987.tb02504.x.
The chicken lysozyme gene is constitutively expressed in macrophages. Transfection of recombinant genes containing different portions of the lysozyme 5' upstream region revealed the existence of two negative transcriptional elements within 1 kb upstream of the start sites. Both elements placed upstream or downstream of a heterologous promoter-gene unit repress transcription independent of their orientation and are therefore called silencer elements, although their repressing activities 3' of the gene are reduced. One silencer (N-1.0 kb) at position -1 kb consists of the central region of the chicken middle repetitive sequence element CR1 and can be divided into two functional domains. N-1.0 kb is active in all cell types tested. The other silencer (N-0.25 kb) at position -0.25 kb shows reduced activity in primary macrophages. Despite their different specificities, the activity of both silencer elements can be influenced similarly. An inverse linear relationship between the transcriptional activity of the tested constructs and the potential inhibition by the silencer elements was found: weak transcription units can be strongly repressed, whereas strong transcription units can be only weakly repressed. Such a mechanism may help to turn off completely a particular gene in situations or tissues where strong positive regulators are inactive.
鸡溶菌酶基因在巨噬细胞中组成性表达。转染含有溶菌酶5'上游区域不同部分的重组基因，发现在起始位点上游1 kb范围内存在两个负转录元件。这两个元件置于异源启动子 - 基因单元的上游或下游时，均可独立于其方向抑制转录，因此被称为沉默子元件，尽管它们在基因3'端的抑制活性有所降低。位于 -1 kb处的一个沉默子（N - 1.0 kb）由鸡中间重复序列元件CR1的中心区域组成，可分为两个功能结构域。N - 1.0 kb在所有测试的细胞类型中均有活性。另一个位于 -0.25 kb处的沉默子（N - 0.25 kb）在原代巨噬细胞中的活性降低。尽管它们具有不同的特异性，但两种沉默子元件的活性受到的影响相似。在所测试构建体的转录活性与沉默子元件的潜在抑制作用之间发现了一种反向线性关系：弱转录单元可被强烈抑制，而强转录单元只能被弱抑制。这种机制可能有助于在强正调控因子无活性的情况或组织中完全关闭特定基因。
