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From 2010.igem.org

Promoters

NsrR, NarK, NsrX? All the promoters we considered, why we decided to use the one we did

The NsrR Repressor and PyeaR Promoter

NsrR is a regulatory protein that regulates the transcription of a number of operons in E. coli, mostly these code for genes that are associated with nitrate metabolism, though there is also evidence that it plays a role in regulating motility in certain strains of E. coli [10].

NsrR was first identified in Nitrosomonas europaea, a lithoautotropic bacterium. N. europaea is capable of acquiring free energy via the aerobic oxidation of ammonia to nitrite, as well as using nitrate and nitrite as alternative electron acceptors in an anaerobic environment. NsrR was reported as being a nitrite sensitive repressor of the nitrite reductase NirK, it is thought to protect

N. europaea against the toxic affects of N O2 produced during nitrification [11]. There is also evidence from the human pathogen Neisseris meningitidis that NsrR reacts to nitric oxide [12].

NsrR is a member of the Rrf2 family of transcription factors, this is a family of transcription factors mostly involved in nitrate and iron metabolism, and nitric oxide detoxification. NsrR has been shown to regulate the response of E. coli to reactive nitrogen species [13], specifically to nitrite and nitric oxide [6], [14]. It regulates the response by both repressing and activating operons. Filenko et al. [13] reported 20 repressed genes and 24 activated genes.

The promoter that was used in conjunction with NsrR is from the yeaR-yoaG operon, PyeaR. This was identified by Filenko as a gene that is repressed by NsrR, though they also predicted that it was co-regulated by an oxygen responsive transcription factor Fnr. It was shown by Lin et al. [5] that its transcription is actually independent of this factor. This is important because the Fnr transcription factor is associated with E. coli ’s anaerobic metabolism, meaning that the metabolic state of the E. coli would have to be controlled if it were to act as a sensor. Using the PyeaR promoter avoids this restriction.