Zacharias M, Wagner R
Max-Planck-Institut für Molekulare Genetik, Abteilung Wittmann, Berlin, FRG.
Mol Microbiol. 1989 Mar;3(3):405-10. doi: 10.1111/j.1365-2958.1989.tb00185.x.
Transcription of ribosomal RNAs in Escherichia coli is started from two strong tandem promoters, P1 and P2. It is known, however, that internal promoter-like structures occur and in a recent report (Mankin et al., 1987) a promoter sequence Pi within the 16S and 23S RNA spacer region showing good homology to the prokaryotic consensus promoter structure was identified. It was proposed that this putative promoter has a possible function in the transcription of ribosomal RNAs in E. coli. Fusion of various DNA fragments containing the putative promoter sequence and different parts of the 16S/23S spacer region as well as the 23S RNA to the galactokinase gene allowed us to assess the functional activity of the promoter in vivo. To determine any growth rate dependent function of the putative promoter, the measurements were performed under different growth conditions. The promoter activity did not exceed 7% of the lac promoter under in vivo assay conditions. In addition, transcription starting at the promoter Pi did not proceed through the entire 23S RNA gene. We conclude, therefore, that transcription from Pi does not contribute significantly to the synthesis of ribosomal RNAs. Thus its functional significance, if any, remains elusive.
大肠杆菌核糖体RNA的转录起始于两个紧密串联的启动子P1和P2。然而，已知存在内部启动子样结构，并且在最近的一份报告中（曼金等人，1987年），在16S和23S RNA间隔区中鉴定出一个启动子序列Pi，它与原核生物共有启动子结构具有良好的同源性。有人提出，这个假定的启动子在大肠杆菌核糖体RNA的转录中可能具有某种功能。将含有假定启动子序列以及16S/23S间隔区不同部分和23S RNA的各种DNA片段与半乳糖激酶基因融合，使我们能够在体内评估该启动子的功能活性。为了确定假定启动子的任何生长速率依赖性功能，在不同的生长条件下进行了测量。在体内测定条件下，该启动子的活性不超过lac启动子的7%。此外，从启动子Pi起始的转录并未贯穿整个23S RNA基因。因此，我们得出结论，从Pi起始的转录对核糖体RNA的合成贡献不大。因此，其功能意义（如果有的话）仍然难以捉摸。
