Schnetz K
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
EMBO J. 1995 Jun 1;14(11):2545-50. doi: 10.1002/j.1460-2075.1995.tb07252.x.
Silencing of a transcriptional unit by flanking sequence elements has so far only been described for eukaryotic systems. Here, a similar system is described in bacteria. The Escherichia coli bgl operon (beta-glucoside utilization) is normally cryptic due to very low promoter activity. However, low activity is not attributable to the quality of the promoter itself but is caused by its chromosomal context. The bgl promoter is perfectly active when tested outside of its normal context of a stretch of a few hundred base pairs. In addition, other promoters become inactivated when placed into the bgl region. Both the deletion of an upstream sequence element and the replacement of sequences located downstream result in promoter de-repression, demonstrating that silencing of promoters within this stretch of DNA in vivo is an active process brought about by the combined action of upstream and downstream chromosomal elements.
到目前为止，侧翼序列元件对转录单元的沉默作用仅在真核生物系统中被描述过。在此，我们描述了一种细菌中的类似系统。大肠杆菌的bgl操纵子（β-葡萄糖苷利用）由于启动子活性非常低，通常处于沉默状态。然而，低活性并非归因于启动子本身的质量，而是由其染色体环境导致的。当在其正常的几百个碱基对的延伸区域之外进行测试时，bgl启动子具有完全活性。此外，其他启动子被置于bgl区域时会失活。上游序列元件的缺失和下游序列的替换都会导致启动子去抑制，这表明在体内这段DNA中启动子的沉默是由上游和下游染色体元件的共同作用引起的一个主动过程。
