Almond N, Yajnik V, Svec P, Godson G N
Biochemistry Department, NYU Medical Center, NY 10016.
Mol Gen Genet. 1989 Apr;216(2-3):195-203. doi: 10.1007/BF00334356.
The Escherichia coli rpsU-dnaG-rpoD operon contains an internal transcription terminator T1 located in the intergenic region between the rpsU and dnaG genes (Smiley et al. 1982). By cloning T1 as a small 127 bp fragment into the terminator probe plasmid pDR720 between the trp operator promoter and the assayable galK gene, it was shown that T1 acts as a strong transcription terminator, comparable in strength to the 3' operon terminator T2. However, an operon sequence that occurs 5' to T1 within the coding region of the rpsU gene and which has homology with the lambda nut site, (Lupski et al. 1983) when placed 5' to T1 in the pDR720 plasmid construct, modifies transcription through T1 allowing expression of the galK gene. This sequence, called the dnaG nut site also modifies the termination activity of the external operon terminator T2. It is proposed that the dnaG nut site is a cis-acting element of an antitermination system in E. coli.
大肠杆菌的rpsU - dnaG - rpoD操纵子含有一个位于rpsU基因和dnaG基因之间基因间隔区的内部转录终止子T1（斯迈利等人，1982年）。通过将T1作为一个127 bp的小片段克隆到终止子探针质粒pDR720中，置于色氨酸操纵子启动子和可检测的半乳糖激酶基因之间，结果表明T1作为一个强转录终止子，其强度与3'操纵子终止子T2相当。然而，rpsU基因编码区内T1上游出现的一段操纵子序列，与λ噬菌体的nut位点具有同源性（卢普斯基等人，1983年），当将其置于pDR720质粒构建体中T1的上游时，可改变通过T1的转录，使半乳糖激酶基因得以表达。这个序列，称为dnaG nut位点，也会改变外部操纵子终止子T2的终止活性。有人提出，dnaG nut位点是大肠杆菌中一种抗终止系统的顺式作用元件。
