Part:BBa_K3098021

Omp Promoter + riboswitch/sfGFP

The promoter pOmpC is positively regulated, OmpR-controlled promoter (from Part: BBa_R0082 ). This promoter is taken from the upstream region of OmpC. Phosphorylated OmpR binds to the three operator sites and activates transcription. Its expression is related to the osmotic pressure. In nature, this promoter is upstream of the OmpC porin gene. The regulation of OmpC is determined by the EnvZ-OmpR osmosensing machinery. EnvZ phosphorylates OmpR to OmpR-P. At high osmolarity, EnvZ is more active, creating more OmpR-P. OmpR-P then binds to the low-affinity OmpR operator sites upstream of ompC.

But we found that, this promoter can be used not only for its osmosensing function, in some other condition, it is also be used as a part of a system, such as the red light system ( from Part: BBa_K1017301BBa_K1017301 ). In such condition, we hope to get rid of the influence of the osmosis, thus, we create a new part by adding a riboswitch after the promoter, to realize another kind of control via theophylline.

Usage and Biology

This part better to be expressed in DH5α, because the EnvZ-OmpR is a protein naturally expressed in K-12 strain. And the unprocessed state of this part is off, because when there are id no theophylline, the riboswitch is turned off. When you want it to be on and start to express the target gene, you have to add the theophylline to open the riboswitch. Thus we achieved the tightly control of this promoter via a riboswitch.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 822
  

Functional Parameters

Two experiments were did to confirm the tightly control of this new part.

Firstly, transform the plasmids of pOmpC with a sfGFP and pOmpC+ribo with a sfGFP into DH5α. When the ranged between 0.6~0.8, we move them into different LB fluid medium had different osmotic pressure in order to verified the close effect of riboswitch. The result (Fig.1) is that the pOmpC with riboswitch had lower fluorescence value than pOmpC. What’s more, the amplitude of variation  of pOmpC is greater than pOmpC with ribo, which means that adding the riboswitch can decrease the influence by osmotic pressure for the promoter pOmpC.
<center> </center> <center> Under the best osmosis condition of pOmpC + ribo (0.1% NaCl), Theophylline is added to the final concentration from 0mM - 8mM. When the concentration of theophylline between 0 -2 mM, the promoter pOmpC with riboswitch did not open, but when it came to 4mM, the fluorescence value increased significantly.
<center> </center> <center>