Difference between revisions of "Part:BBa K1639014"

Revision as of 09:25, 22 September 2015

TnrA-pAlsT-mRFP reporter system

Main goal of this part is to show TnrA protein’s repressor activity on pAlst promoter and derepression of this promoter in the presence of NH3. Thereby we combined TnrA protein’s and pAlst’s gene sequences on the same biobrick. As a reporter, we put RFP gene sequence in front of the pAlst sequence. To make sure the repressive protein TnrA is produced in a high amount, we combined TnrA-pAlst-RFP gene sequence with T7 promoter which has a high transcription rate.

Usage and Biology

Figure 1: If there is a sufficient amount of NH3, Toehold and TEV protease will be produced. If there isn’t a sufficient amount of NH3, Toehold and TEV Protease will not be produced.

Bacteria use nitrogen which is present in nearly all macromolecules such as proteins, carbonhydrates and peptidoglycan. Prokaryotes have developed transport and assimilation systems for a variety of nitrogen sources for living under optimal conditions and regulate their own systems. This regulatory network allows an adequate response to situations of nitrogen limitation.

In the Bacillus subtilis, ammonium assimilation occurs via the glutamine synthetase - glutamate synthase pathway. Bacillus subtilis faces nitrogen- limiting conditions when it consumes glutamate as a prior nitrogen source, while glutamine is the secondly preferred nitrogen source [3].

Two transcription factors, TnrA and GlnR, and one enzyme, the Glutamine Synthase, are the major players in the B. Subtilis nitrogen regulatory network [3]. We use TnrA transcription factor in our system.

Under nitrogen-limited conditions, TnrA works as an activator and a repressor both. TnrA represses expression of glnRA (Glutamine Synthase) [4], gltAB (Glutamate Synthase) [5] and other genes. Also the form of Glutamine Synthase which is feedback inhibited by excess glutamine, directly interacts with and unbinds from TnrA, thus blocks its DNA-binding activity [6]. Based on all this information, if the amount of NH3 is not sufficient, glutamine synthase will not work properly, glutamine will be produced in a low amount, TnrA will bind to promoter and Toehold production will be repressed. But if there is a sufficient amount of NH3, glutamine will be produced in a high level, TnrA will not repress the promoter as previous and Toehold – Tev Protease will be produced in a high amount.

Seventeen TnrA targets were detected by a combination of DNA microarray hybridization, a genome-wide search for TnrA boxes, and gel retardation assays [7]. The TnrA box consensus delimited in this study to a 17- bp interrupted, inverted repeat sequence, TGTNANAWWWTNTNACA.

Characterization

Sequence and Features

References