Architecture of Bacterial Promoters; The case of the Escherichia coli ogt Promoter

摘要

All bacteria utilize RNA polymerase enzyme and transcription activator proteins to regulate gene expression in response to internal or external stress. Some bacterial promoters are regulated with only one transcription factor whilst two or more transcription activators regulate some other promoters. NarL is a transcription activator protein that activates the E. coli yeaR and ogt promoters in response to nitrate and nitrite induction in absence of oxygen. In the present study we have studied ogt1052 promoter, which is a derivative of ogt promoter containing only one NarL binding site very close to -35 element. Therefore, it is considered as class II activator dependent promoter just as yeaR promoter. A molecular structure of ogt1052 promoter was proposed which suggests that NarL binding site is located in opposite face of DNA that contains Alpha-CTD and sigma domain 4 of RNA polymerase enzyme required for promoter recognition. The aim of the present study was to study and test the suggested molecular model by creating point mutations at -35 element and deletion of one base pair in spacer region, to test whether sigma domain 4 is necessary to bind -35 hexamer in order to start transcription initiation, and to test whether NarL activates the promoter by interaction with Alpha-CTD in the opposite face of the DNA. Based on the result achieved, ogt1052 promoter is a class I promoter “dressed” like a class II promoter.