Part:BBa_K2970006

Gate Composition

This gate is a toehold switch system with which a gene of interest can be locked and regulated on a translational level using mRNA as regulator. After transcription, the mRNA of this gate forms a hairpin that hides the ribosome binding site and start codon of the gene of interest, thus translation can not occur. A complementary part to the gate (trigger) is needed to open the hairpin and release the ribosome binding site. In this case two triggers are needed that form a trigger complex to open the gate (BBa_K2970000 and BBa_K2970001). The affinity between the trigger complex and the gate is greater than that of the gate to itself (in the loop). A single trigger cannot open the gate because it has only half the required complementary sequence.

To use this system in bacteria we implemented the gate sequence together with a gene for chloramphenicol (BBa_K2970011), flanked by a constitutive promoter (BBa_J23100) and a strong terminator (BBa_B1002) into pSB1A3 where the ampicillin resistance can be cut out.

After transformation of both trigger plasmids (BBa_K2970003 and BBa_K2970004) and the gate plasmid in one bacterium all three mRNA structures will be formed, the gate will be opened, and the translation of the chloramphenicol resistance can take place. Bacteria that took all three plasmids are able to survive on media with chloramphenicol. This system can be used to transform many genes of interest on three different plasmids into bacteria with only using one antibiotic resistance instead of three different resistances.

Usage and Biology

This part can be used together with both trigger compositions for triple transformation in bacteria. Genes of interest that should be transformed together, can be put on the three plasmids. Only if all three plasmids are taken by a bacterium the chloramphenicol resistance is produced and the bacterium can survive on medium with chloramphenicol. Thus chloramphenicol can be used to select for bacteria that got all genes of interest.

Results

We tested this part by performing triple transformations of this part on pSB1A3 together with both trigger compositions, on pSB1A3 backbones as well. After transformation we selected by plating the bacteria on plates with chloramphenicol. We compared the results with positive and negative controls. Furthermore we did single transformation of each part to measure how leaky the gate is.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 7
  Illegal NheI site found at 30
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]