Tesfa-Selase F, Drabble W T
Department of Biochemistry, University of Southampton, England.
Eur J Biochem. 1996 Oct 15;241(2):411-6. doi: 10.1111/j.1432-1033.1996.00411.x.
Expression of the guaBA operon of Escherichia coli is regulated by the DNA replication-initiating protein, DnaA. Two DnaA boxes, which are potential binding sites for DnaA, are present in the gua operon. One box (with 8/9 match to the DnaA box consensus sequence) is at the gua promoter; the other box, which has a consensus sequence, is on the non-transcribed strand within the guaB coding region approximately 200 bp downstream of the initiation codon. The binding in vitro of purified DnaA protein to these boxes was investigated by filter retention and gel retardation analysis, and by deoxyribonuclease I footprinting, using restriction fragments of gua operon DNA. DnaA protein was shown to bind specifically only to the fragment carrying the consensus sequence DnaA box, and to protect this box from deoxyribonuclease I. Transcription termination resulting from the binding of DnaA to this box within the guaB gene explains repression by DnaA of the gua operon in vivo.
大肠杆菌guaBA操纵子的表达受DNA复制起始蛋白DnaA的调控。gua操纵子中存在两个DnaA框，它们是DnaA的潜在结合位点。一个框（与DnaA框共有序列有8/9匹配）位于gua启动子处；另一个具有共有序列的框位于guaB编码区内起始密码子下游约200 bp处的非转录链上。使用gua操纵子DNA的限制性片段，通过滤膜滞留和凝胶阻滞分析以及脱氧核糖核酸酶I足迹法研究了纯化的DnaA蛋白在体外与这些框的结合。结果表明，DnaA蛋白仅特异性结合携带共有序列DnaA框的片段，并保护该框免受脱氧核糖核酸酶I的作用。DnaA与guaB基因内该框的结合导致的转录终止解释了DnaA在体内对gua操纵子的抑制作用。
