Part:BBa_K1065302

Blue light sensing device without inverter for the production of amilGFP

This part includes the promoter pLac and BBa_K1065305, the improved version of the Blue light sensor device BBa_K952003 (see details in Design notes). In the presence of blue light (470 nm) the production of the reporter amilGFP is inhibited. In the absence of blue light the device is activated, thus producing amilGFP [1]. The whole system is under the control of a constitutive promoter pLac.
This part was cloned and successfully characterized by UNITN-Trento 2013 iGEM team in order to test protein production and then add an ethylene forming enzyme (EFE) after amilGFP.

SAFETY NOTES: this part does not present safety issues.

Usage and Biology

YF1, the blue light sensor, is a fusion protein made of the LOV blue light sensor domain of Bacillus subtilis (YtvA) and FixL histidine kinase domain from Bradyrhizobium japonicum [2]. In the dark, YF1 autophosphorylates and successively phosphorylates FixJ, its Response Regulator, which in turn activates the pFixK2 promoter [3] allowing amilGFP transcription .
Under constant illumination with blue light, net kinase activity is strongly repressed, resulting in the inactivation of pFixK2: amilGFP is no longer produced [1].

We characterized this part in E. coli using cells NEB10β.

induction test: successful improvement of the part and defined light dependent ON/OFF switch

To determine whether inserting an RBS after pFixK2 would actually improve the part (BBa_K952003) we characterized both our improved part and the original one, testing them under the same conditions. The improved part actually behaved as expected, producing the yellow fluorescent protein in the dark and not under illumination. Conversely, BBa_K1065300 (constituted by the original part BBa_K952003 and pLac) did not work in both cases, indicating that the original part doesn't work properly and that we effectively improved it.

Figure 1. Improved part and original part after induction: one culture of E. coli (strain NEB10β) transformed with BBa_K1065302 and one culture with BBa_K1065300, were grown until an OD of 0.7. Each culture was then split in two 10 ml samples (dark and light). Cells were kept O/N in glass culture tubes at 37°C under shaking. Cultures were then centrifuged and cell pellets were compared. A different coloration in the Bba_K1065302-transformed sample kept in the dark (1) was observed when compared to the blue light exposed control (2) and the samples without RBS (3 and 4). .

Fluorescence measurements confirms previuos testing

After induction, 10 ml of cultures were pelleted, resuspended in 2 ml of PBS, and sonicated. The supernatant was used to measure fluorescence spectra. Excitation and emission wavelengths were 503 nm and 512 nm, respectively. All measurements were taken with a Cary Eclipse Varian fluorimeter.

Figure 2. Fluorimetric spectra: Dark-induced cultures of BBa_K1065302 (purple) produced the greatest amount of chromoprotein; Cultures of BBa_K1065302 exposed to light showed a basal expression of amilGFP (green). As expected the part without RBS, BBa_K1065300 showed no activity both in the dark (blue) and under illumination (red). Our part with RBS is undeniably improved and works as expected. Cells were grown as described in figure 1.

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
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 770
  Illegal NgoMIV site found at 842
  Illegal NgoMIV site found at 932
  Illegal NgoMIV site found at 950
  Illegal NgoMIV site found at 1462
  Illegal NgoMIV site found at 1755
  Illegal NgoMIV site found at 1849
  Illegal AgeI site found at 484
  Illegal AgeI site found at 1630
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 1519
  Illegal BsaI.rc site found at 383
  

References

1. Alieva, N. O., et al. 2008. Diversity and evolution of coral fluorescent proteins. PLoS One 3:e2680.
2. Moglich A, Ayers RA and Moffat K. (2009) Design and Signaling Mechanism of Light-Regulated Histidine Kinases. J. Mol. Bio. 385, 5, 1433-1444.
3. Ohlendorf, R., Vidavski, R.R., Eldar, A., Moffat, K. & Möglich, A.(2012). From Dusk till Dawn: One-Plasmid Systems for Light-Regulated Gene Expression. J. Mol. Biol., 416: 534: 542