RBS (B0034) + MerR (mercury-responsive transcription factor)
The native RBS of MerR is not strong enough and its intensity can not be predicted as there is no such a corresponding RBS part in Registry. In order to facilitate the use and further characterization of MerR for future teams, we prefixed an RBS part BBa_B0034 from Partsregistry.
The model of MerR controlling PmerT tracscription indicates that the apo-merR and Hg-bound merR have a competition. We speculate that the threshold of MerR response can be also manipulated by controlling the concentration of MerR in cytosol. As with the bacteria in natural environment, the concentration of MerR is stabilized at a certain level. In our design, merR was isolated from the operon and assembled with constitutive promoters of certain strength to maintain its expression intensity at certain level, then the sensitivity of PmerT under different MerR concentrations can be denoted by mercury threshold concentration at which reporter (GFP) expression emerges. (Fig.3).
Fig.3. The construction of bioreporter.
We observed that cells with different MerR intensity exhibited correspondingly different sensitivity to mercury. Namely, the stronger the expression intensity of MerR is, the higher threshold will be represented(Fig.4).
Fig.4. The expression intensity of MerR significantly determines the threshold of response to mercury (II). Five representative lines are selected and it can be observed that the threshold has varied apparently. The letter in the bracket after each promoter name denotes the backbone (pSB3K3 or pSB1A2) where Pc-RBS-merR was cloned into. The deeper the colour represents, the stronger the expression level of MerR is, leading to a higher threshold.
- 10COMPATIBLE WITH RFC
- 12COMPATIBLE WITH RFC
- 21COMPATIBLE WITH RFC
- 23COMPATIBLE WITH RFC
- 25COMPATIBLE WITH RFC
- 1000COMPATIBLE WITH RFC
The coding sequence of MerR comes from Tn21, prefixed by an RBS part BBa_B0034 from Partsregistry
Brown, N. L., J. V. Stoyanov, et al. (2003). "The MerR family of transcriptional regulators." FEMS Microbiol Rev 27(2-3): 145-163.
Hobman, J. L., J. Wilkie, et al. (2005). "A design for life: prokaryotic metal-binding MerR family regulators." Biometals 18(4): 429-436.
Diana M. Ralston, Tomas V. O'Halloran, et al. (1990). “Ultrasensitivity and heavy-metal selectivity of the allostericalyl modulated MerR transcription complex” Proc. Natl. Acad. Sci. USA, Vol. 87, pp. 3846-3850,
Park, S. J., J. Wireman, et al. (1992). "Genetic analysis of the Tn21 mer operator-promoter." J Bacteriol 174(7): 2160-2171.