Insight into the Molecular Mechanism of the Transcriptional Regulation of amtB Operon in Streptomyces coelicolor

Zhendong Li, Xinqiang Liu, Jingzhi Wang, Ying Wang, Guosong Zheng, Yinhua Lu, Guoping Zhao, Jin Wang

InStreptomyces coelicolor,amtBtranscription is promptly regulated by the global nitrogen regulator GlnR. Although the GlnR bindingcis-element has been characterized inamtBpromoter, consisting of three GlnR boxes ofa3-b3,a1-b1, anda2-b2, 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 inamtBpromoter (i.e.,a3-b3,a1-b1, anda2-b2sites), and GlnR was able to binda3-b3anda1-b1, respectively, but nota2-b2alone. Consistently,a2was not a typical GlnR binding site and further experiments showed thata2was non-essential for GlnR-mediated bindingin vitroand transcriptional regulationin vivo. To uncover the physiological role of the three GlnR boxes, we then mutated the wild-typeamtBpromoter to a typical GlnR-binding motif containing two GlnR boxes (a3-b3-a2-b2), 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 activatingamtBtranscription in response to nitrogen limitation, facilitating bacterial growth under nitrogen stresses.