Difference between revisions of "Part:BBa K568001"

Revision as of 16:14, 29 September 2011

Optogenetical AND-Gate red/blue light

This logical gate is based on amber stop-codon suppression via the non-canonical tRNA supD (BBa_K228001). The blue light sensor (BBa_K238013) induces the expression of a mRNA coding for a T7-polymerase with an amber mutation (BBa_K228000), that can only be translated by ribosomes if the correct supD tRNA is present. The supD tRNA is expressed when the red light sensor (BBa_K568000) is induced. Thus, only cells which receive both signals produce the desired substances. Cells need to be transfected with another plasmid, containing a T7 promoter.

Usage and Biology

If the part is hit by both far red light (705 nm) and blue light (465 nm) beams, the AND-Gate is turned on. Red light induces the autophosphorylation at the cytosolic site of cph8. This leads to phosphorylation of OmpR which subsequently binds to OmpC promotor and enables transcription of the supD t-RNA. Blue light leads to dimerisation of YcgF and binding of the repressor YcgE. The formation of the YcgE-YcgF complex leads to the unbinding of YcgE from the YcgZ promoter which activates the transcription of T7ptag (T7 polymerase with the amber stop codon mutation) if enough supD tRNA is available.

This AND-gate should ensure that expression of T7 polymerase is only induced when both wavelengths hit bacteria with the part.

Sequence and Features

Functional Parameters

Induction with red light at 705 nm

Induction with blue light at 465 nm

Shut down of constant red light signalling with 650 nm

Experimental Testing

The part was tested using the following setup:

K568001 (in vector pSB1C3) and Part:BBa_I746907 (as a GFP-based reporter, in vector pSB6A1) were electroporated into e. coli CP919. A clone from the transformation was picked and incubated over night in LB (Amp, Cam) under red light (650 nm) to shut down the and-gate. The next day, the culture was diluted with LB (Amp, Cam) to an initial OD600 of approx. 0.2, and divided into three parts. These three groups were incubated under three different lighting conditions:

• in the dark
• under red (705 nm) and blue (465 nm) light (using LEDs)
• under the lamp of the incubator (white light).

The expression of GFP was measured using a GFP assay as follows: Over the next 6 hours, the OD600 and the GFP-fluorescence was measured (time between measurements: 1 hour). 16 hours after the last measurement, the terminal OD600 and GFP-fluoresence were measured. Also, serveral measurements of LB-Medium as blank were done. To get information about the "fluorescence per cell", the following formula was used:

"Fluorescence per cell" = (fluorescence(sample) - fluorescence(blank)) / (OD600(sample) - OD600 (blank))

The diagram shows that the cells incubated under white light (which contains the necessary blue and red wavelengths for induction) express GFP at a significantly higher level than those incubated under red and blue LEDs or in the dark. Since the light was the only difference of incubation conditions, it is the reason for the higher amount of GFP. This shows that the optogenetical AND-Gate works as expected. The fact that the cells incubated under red and blue LEDs did not produce a similar amount of GFP could be due to the lower light intensity of the LEDs compared to the intensity of the white light bulb.