Activity of two different silencer elements of the chicken lysozyme gene can be compensated by enhancer elements.
Activity of two different silencer elements of the chicken lysozyme gene can be compensated by enhancer elements.
复制标题
鸡溶菌酶基因的两个不同沉默元件的活性可以通过增强元件来补偿。
作者：
Aria Baniahmad;Marc Muller;C. Steiner;Rainer Renkawitz
鸡溶菌酶基因在巨噬细胞中组成型表达。重组基因的转染结果表明，在溶菌酶5′上游1 kb内存在两个负转录元件。位于异源启动子-基因单元上游或下游的两个元件抑制转录，而与它们的方向无关，因此被称为沉默元件，尽管它们对基因3′端的抑制活性降低。一个位于-1 kb的沉默子（N-1.0 kb）由鸡中间重复序列元件CR 1的中心区域组成，可分为两个功能结构域。N-1.0 kb在所有检测的细胞类型中均具有活性。在-0.25 kb位置的另一个沉默子（N-0.25 kb）在原代巨噬细胞中显示出降低的活性。尽管它们的特异性不同，但两种沉默元件的活性可以受到类似的影响。发现测试构建体的转录活性与沉默元件的潜在抑制之间存在逆线性关系：弱转录单位可以被强烈抑制，而强转录单位只能被微弱抑制。这种机制可能有助于在强阳性调节因子不活跃的情况下或组织中完全关闭特定基因。
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.