Insight into the Molecular Mechanism of the Transcriptional Regulation of Operon in .

In , transcription is promptly regulated by the global nitrogen regulator GlnR. Although the GlnR binding -element has been characterized in promoter, consisting of three GlnR boxes of , , and , its role in GlnR-mediated transcriptional regulation remains unclear. Here, we showed that GlnR had different binding affinity against each pair of GlnR binding sites in promoter (i.e., , , and sites), and GlnR was able to bind and , respectively, but not alone. Consistently, was not a typical GlnR binding site and further experiments showed that was non-essential for GlnR-mediated binding and transcriptional regulation . To uncover the physiological role of the three GlnR boxes, we then mutated the wild-type promoter to a typical GlnR-binding motif containing two GlnR boxes (), and found although the transcription of the mutated promoter could still be activated by GlnR, its increasing rate was less than that of the wild-type. Based on these findings, one could conclude that the three GlnR boxes assisted GlnR in more promptly activating transcription in response to nitrogen limitation, facilitating bacterial growth under nitrogen stresses.