Melbourne/Blue Photosensor


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As part of the overall system design, a blue light sensitive pathway is required in addition to the red light sensitive pathway. Described below is the blue photosensor. This involves the design of a chimeric trans-membrane protein. A blue light sensitive (~500nm) integral photo receptor SopII that dimerizes with a histidine kinase; HtrII (As described in 2001 paper).

The kinase domain of HtrII will be replaced with the kinase domain of ComP. ComP forms part of a two-component system from Bacillus subtilis - and this will not affect any endogenous networks in e.coli. The two component system involves: ComP, a two-component sensor histidine kinase and ComA, a two-component response regulator. Phosphorylated comA will upregulate transcription at the psfA/srfA promoter psfA/srfA, as part of the AND gate.

In summary:

SrII-HtrII + ComP >>>>>> HtrII-ComP fusion


Blue Photosensor Background


Possible extensions:

  • Determination of optimal wavelength:
    • use of different substrates (different retinals)
  • Separate variants all submitted as BioBricks.
  • Submitted synthesized ComP and ComA as BioBricks
  • Model the pathway to determine rate-limiting step


This part is based on “Photostimulation of a Sensory Rhodopsin II/HtrII/Tsr Fusion Chimera Activates CheA-Autophosphorylation and CheY-Phosphotransfer in Vitro” by Vishwa D. Trivedi and John L. Spudich, Biochemistry 2003, 42, 13887-13892. Acording to this article the peak sensitivity is to 500+/-5nm, and results in a 3 fold activation of the Tsr (wild type). CheA,W,Y connected system.

It is proposed to replace Tsr fusion with homolgouse ComP. SRII-HtrII fusion to which ComP is fused ComA when phosphorylated by ComP is an activator for PsfA promoter sequence from Dr Alan Grossman (M.I.T.) Based on

  • SRII-HtrII-Tsr fusion from Prof J.L. Spudich (university of Texas)melb:spudich N sequence
  • BBa_J51000 (ComP) kinase
  • BBa_J51001 (ComA) activator


  • SrfA promoter
  • ComA protein generator
  • SRII-ComP photosensor
  • Any phyco construction genes?

SRII is from Natronomonas pharaonis.

Tsr fusion was made by Jung et al J Bacteriol 183 6365-6371 (2001) they propose a mechanism.