Part:BBa_K1031941

Pm-B0034-eGFP (XylS)

For detailed information concerning XylS and Pm promoter, please visit 2013 Peking iGEM Biosensor XylS

Structure

XylS is the activator of Pm promoter, which is σ-54 dependent. XylS recognizes two 15-bp repeats (TGCA-N6-GGNTA) in Pm promoter, each featured by box A1/A2 (TGCA) and box B1/B2 (GGNTA), respectively. The arrangement of the two repeats is deposited as shown in Fig 1; the proximal XylS binding site overlaps the -35 box by 2 bp (the sequence for the binding of RNA polymerase)(Fig 1 a, b)

Fig 1 Sequence features of Pm. promoter The orange arrows indicate the two XylS binding sites (proximal and distal), each consisting of conserved A1/A2 and B1/B2 boxes. The -10 and -35 hexamers are in blue. A right-angled arrow indicates the transcription start site (+1).

Sequence and Features

Assembly Compatibility:

10
COMPATIBLE WITH RFC[10]
12
INCOMPATIBLE WITH RFC[12]
Illegal NotI site found at 38
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 750

Construction and data

K1031941 is composed of three elements, the inducible promoter Pm, RBS (Ribosome Binding Site) B0034, and reporter gene eGFP with terminator B0015. (Fig 2)

Fig 2 Construction of reporter circuit. The orange arrow represents Pm promoter for XylS. The green oval stands for RBS B0034. eGFP coding sequence is shown with dark blue, while terminator B0015 is in dark red.

We tested this reporter circuit with different expression intensity of XylS coding sequence and selected the optimal-performed biosensor circuit composed of J23114-XylS and Pm-B0034-eGFP, then this circuit is subjected to ON/OFF test with 78 aromatic compounds, characterizing XylS detecting profile.(Fig 3)

Fig 3 The induction ratios of all 78 typical aromatic compounds in the ON/OFF test following Test Protocol 1. XylS biosensor could respond to 24 out of 78 aromatics with the induction ratio higher than 20, mainly benzoate, salicylic and their derivatives.

Dose-response curve is plotted to further characterize XylS performance with efficiency inducers at different concentration, proving that biosensor circuit Pm/J23114-XylS performs like Hill function.

Fig 4 Dose-response curves of XylS biosensor induced by benzoate and its derivatives. X-axis stands for concentration gradient of inducers at 10µM, 30µM, 100µM, 300µM and 1000µM. Different colors represent different kinds of inducers. Y-axis shows induction ratios. The induction ratio was calculated by dividing the fluorescence intensity of biosensor exposed to object inducers by the basal fluorescence intensity of the biosensor itself.