Regulatory

Part:BBa_J23100:Experience

Designed by: John Anderson   Group: iGEM2006_Berkeley   (2006-08-04)

This experience page is provided so that any user may enter their experience using this part.
Please enter how you used this part and how it worked out.

Applications of BBa_J23100

Sheffield 2016 Review

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Sheffield 2016 has improved the characterisation of both BBa_J23100 and BBa_J23106. These parts are a strong and medium promoter respectively, that we have used to design our iron detecting device. We have experimentally validated through fluorimetry that there is indeed a significant difference between expression levels of GFP coupled to the strong and medium promoters. Comparative analysis of promoter strengths can be directly interpreted from the data we obtained. This data can be found both on the original part experience pages of BBa_J23100 and BBa_J23106, as well as at our website. Our team has also improved the function of the BBa_J23100 part, by adding an RBS site downstream of the promoter (BBa_K2016005). BBa_J23100 was originally submitted to the Registry by Berkeley 2006.

Fluorescence of JC28 mutants or W3110 wild types transformed with RyhB-GFP constructs under the control of medium (MedGFP) or strong promoters (StrGFP).


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ETH Zurich 2014

Characterization of the pLux promoter's sensitivity to 3OC6-HSL depending on LuxR under the promoters J23100, J23111, and J23109

The amount of regulator LuxR (BBa_C0062) in the system was shown to influence the pLux promoter's response to the inducer concentration (3OC6-HSL). By using the three different constitutive promoters BBa_J23100, BBa_J23109, and BBa_J23111 for the production of LuxR we have measured this effect in terms of fluorescence/OD600 (see Figure 1).

Background information

We used an E. coli TOP10 strain transformed with two medium copy plasmids (about 15 to 20 copies per plasmid and cell). The first plasmid contained the commonly used p15A origin of replication, a kanamycin resistance gene, and promoter pLux (BBa_R0062) followed by RBS (BBa_B0034) and superfolder green fluorescent protein (sfGFP). In general, for spacer and terminator sequences the parts BBa_B0040 and BBa_B0015 were used, respectively. The second plasmid contained the pBR322 origin (pMB1), which yields a stable two-plasmid system together with p15A, an ampicillin resistance gene, and one of three promoters chosen from the Anderson promoter collection followed by luxR (BBa_C0062). The detailed regulator construct design and full sequences (piG0041, piG0046, piG0047) are available here.

Experimental Set-Up

The above described E. coli TOP10 strains were grown overnight in Lysogeny Broth (LB) containing kanamycin (50 μg/mL) and ampicillin (200 μg/mL) to an OD600 of about 1.5 (37 °C, 220 rpm). As a reference, a preculture of the same strain lacking the sfGFP gene was included for each assay. The cultures were then diluted 1:40 in fresh LB containing the appropriate antibiotics and measured in triplicates in microtiter plate format on 96-well plates (200 μL culture volume) for 10 h at 37 °C with a Tecan infinite M200 PRO plate reader (optical density measured at 600 nm; fluorescence with an excitation wavelength of 488 nm and an emission wavelength of 530 nm). After 200 min we added the following concentrations of inducers (3OC6-HSL, 3OC12-HSL, and C4-HSL): 10-4 nM and 104 nM (from 100 mM stocks in DMSO). Attention: All the dilutions of 3OC12-HSL should be made in DMSO to avoid precipitation. In addition, in one triplicate only H2O was added as a control. From the the obtained kinetic data, we calculated mean values and plotted the dose-response-curve for 200 min past induction (see Figure 1).

Results

The measurements of the induced system with 3OC6-HSL concentrations of 10-13 M to 10-5 M showed an increasing sensitivity of the pLux (BBa_R0062) promoter (in terms of fluorescence per OD600) for increasing strength of the promoter controlling LuxR (BBa_C0062) expression (see Figure 1). For BBa_J23100 (strongest promoter chosen) the sensitivity is highest (half maximal effective concentration EC50 approximately 20 pM), for BBa_J23109 (weakest one chosen) the sensitivity is lowest (EC50 approximately 100 pM), with BBa_J23111 (medium) falling between these two but closer to the strong promoter (EC50 approximately 10 nM). Overall, this is in line with the promoter strength given in the Anderson collection.


Figure 1 Influence of varied promoter strength on the expression of LuxR (BBa_C0062) and the resulting effect on pLux (BBa_R0062). The fluorescence per OD600 is shown over an inducer-range of 10-13 M to 10-5 M. The promoters used are: BBa_J23100 (high LuxR expression, red), BBa_J23111 (medium LuxR expression, green), and BBa_J23109 (low LuxR expression, blue). All three promoters are part of the Anderson collection. Data points are mean values of triplicate measurements in 96-well microtiter plates 200 min after induction ± standard deviation. For the full data set and kinetics please contact us or visit the raw data page.



The stochastic dynamics of the constitutive promoter family by 2013 Fudan iGEM team

We fused the constitutive promoters to a sfGFP reporter to test their stochastic dynamics by means of measuring fluorescence intensity of sfGFP using flow cytometry. In the meantime, we inserted the 16nt Csy4 insulator between the promoter and the reporter to stardardize the expression of the reporter downstream by eliminating the influence from 5'UTR. The following chart shows the distribution of sfGFP expression in the circumstance of promoter J23100.

Figure 1. The distribution of the sfGFP expression tested by flow cytometry with promoter J23100.
Figure 2. The intensity of different promoters is shown by the column height and the randomness of their functions by the bar width.

Promoter BBA_J23100 efficiency on various strain of E.coli - by iGEM Hong_Kong-CUHK team 2012

To test the expression of sensory rhodopsin triggered by constitutive promoter BBa_J23100 to sense light, we need to test the effect conferred by different E. coli strains to expression of red fluorescence protein reporter downstream of BBa_J23100 to different bacterial strains. It allows us to select the suitable strain(s) for this constitutive promoter for expressing sensory rhodopsin.

Florescence plate reader was used to take readings of fluorescence emission of 635nm and absorbance at 600nm (OD600) between time intervals of 12 hours on each strain. The measurements were started when the cultures reached a OD600 of around 0.4 that represents log phase of active proliferation. Growth curve and fluorescence intensity against time were plotted to compare cell growth and protein expression on different strains.

Three independent experiments were conducted. No significant difference was observed on the growth curves, indicating a similar growth rate among the three bacterial strains with BBa_J23100 transformed. It implies the promoter does not cause cell toxicity or growth inhibition of these three bacterial strains.

Characterization on Bba J23100 OD600.jpg

For the protein expression, the results showed that the fluorescence intensity of reporter in DH5α was significantly lower compared with TOP10 and BL21(DE3).

Characterization on Bba J23100-fluoresence.jpg

To conclude, DH5α is not an optimal strain to utilize promoter BBa_J23100, while TOP10 and BL 21(DE3) can effectively express the reporter. Therefore, in downstream application of our light sensing biobricks (BBa_K786001, BBa_K786002, BBa_K786003) in which BBa_J23100 was used, DH5α are not used.

Evaluation of Anderson promoter J23100 in B. subtilis by iGEM-Team LMU-Munich 2012

This Anderson promoter was evaluated without fused RFP with the lux operon as a reporter in B. subtilis. See the new BioBrick BBa_K823004 without RFP and have a look at the Data from the evaluation in B. subtilis.

Tar receptor under the control of constitutive promoter J23100 by iGEM-Team Göttingen 2012

We mutated the Tar chemoreceptor at in total 5 amino acid sites under the control of constitutive promoter J23100 which are important for ligand binding. The mutated sites are the nucleotides for the amino acids at position 69, 73, 149, 150 and 154 of Tar. Here we used a the constitutive promoter J23100 from the 2006 Berkeley group to test the chemotaxis of E. coli.

For more information: Part:BBa_K777001

Characterization experiment on BBa_J23100, BBa_J23101, BBa_J23118 - UNIPV-Pavia Team (Test performed by L. Pasotti, S. Zucca, E. Del Fabbro)

Description

These three promoters are from the Anderson Promoter Collection, which is a library of constitutive sigma70 bacterial promoters. The strength of each promoter of the library has already been estimated in saturation growth phase cultures in LB, but here we provide the characterization of BBa_J23100 and BBa_J23118 in standard units (RPUs) in LB medium, in order to add experience and data for these BioBricks. BBa_J23101 is the reference standard promoter, so it has RPU=1 for definition.

The data shown below are referred to BBa_K173000, BBa_K173001 and BBa_K173002 that are the measurement parts of BBa_J23100, BBa_J23101 and BBa_J23118 respectively.

Characterization

Compatibility: E. coli TOP10 in pSB1A2

Part LB
Doubling time [minutes] RPU
BBa_J23100
(in BBa_J61002 plasmid)
36 not computed
BBa_J23101
(in BBa_J61002 plasmid)
37 not computed
BBa_J23118
(in BBa_J61002 plasmid)
36 not computed
BBa_K173000 36 2.04 [1.99 ; 2.08]
BBa_K173001 36 1 (reference standard)
BBa_K173002 35 0.69 [0.64 ; 0.73]

BBa_J231xx Growth curves in LB
BBa_J231xx (dGFP/dt)/OD


Growth conditions
Microplate reader experiments
  • 8 ul of long term storage glycerol stock were inoculated in 5 ml of LB + suitable antibiotic in a 15 ml falcon tube and incubated at 37°C, 220 rpm for about 16 hours.
  • The grown cultures were then diluted 1:100 in 5 ml of LB or M9 supplemented medium and incubated in the same conditions as before for about 4 hours.
  • These new cultures were diluted to an O.D.600 of 0.02 (measured with a TECAN F200 microplate reader on a 200 ul of volume per well; it is not comparable with the 1 cm pathlength cuvette) in a sufficient amount of medium to fill all the desired microplate wells.
  • These new dilutions were aliquoted in a flat-bottom 96-well microplate, avoiding to perform dynamic experiments in the microplate frame (see Frame effect section for details). All the wells were filled with a 200 ul volume.
  • If required, 2 ul of inducer were added to each single well.
  • The microplate was incubated in the Tecan Infinite F200 microplate reader and fluorescence (when required) and absorbance were measured with this automatic protocol:
    • 37°C constant for all the experiment;
    • sampling time of 5 minutes;
    • fluorescence gain of 50;
    • O.D. filter was 600 nm;
    • GFP filters were 485nm (ex) / 540nm (em);
    • 15 seconds of linear shaking (3mm amplitude) followed by 10 seconds of waiting before the measurements in order to make a homogeneous culture.
    • Variable experiment duration time (from 3 to 24 hours).
Data analysis
Growth curves

All our growth curves have been obtained subtracting for each time sample the broth O.D.600 measurement from that of the culture; broth was considered in the same conditions of the culture (e.g. induced with the same inducer concentration).

Doubling time

The natural logarithm of the growth curves (processed according to the above section) was computed and the linear phase (corresponding to the bacterial exponential growth phase) was isolated by visual inspection. Then the linear regression was performed in order to estimate the slope of the line m. Finally the doubling time was estimated as d=ln(2)/m [minutes].

In the case of multiple growth curves for a strain, the mean value of the processed curves was computed for each time sample before applying the above described procedure.

Relative Promoter Units (RPUs)

The RPUs are standard units proposed by Kelly J. et al., 2008, in which the transcriptional strength of a promoter can be measured using a reference standard, just like the ground in electric circuits.

RPUs have been computed as:

Pv rpu formula.jpg

in which:

  • phi is the considered promoter and J23101 is the reference standard promoter (taken from Anderson Promoter Collection);
  • F is the blanked fluorescence of the culture, computed subtracting for each time sample fluorescence measure for negative control from that of culture, where the negative control is a non-fluorescent strain (in our experiment it is usually used TOP10 strain bearing BBa_B0032 or BBa_B0033, which are symmply RBSs do not have expression systems for reporter genes);
  • ABS is the blanked absorbance (O.D.600) of the culture, computed as described in "Growth curves" section.

RPU measurement has the following advantages (under suitable conditions)

  • it is proportional to PoPS (Polymerase Per Second), a very important parameter that expresses the transcription rate of a promoter;
  • it uses a reference standard and so measurements can be compared between different laboratories.

The hypotheses on which RPU theory is based can be found in Kelly J. et al., 2008, as well as all the mathematical steps. From our point of view, the main hypotheses that have to be satisfied are the following:

  • the reporter protein must have a half life higher than the experiment duration (we use GFPmut3, BBa_E0240, which has an estimated half life of at least 24 hours, and the experiments duration is always less than 7 hours);
  • strain, plasmid copy number, antibiotic, growth medium, growth conditions, protein generator assembled downstream of the promoter must be the same in the promoter of interest and in J23101 reference standard.
  • steady state must be valid, so (dF/dt)/ABS (proportional to the GFP synthesis rate per cell) must be constant.
Inducible systems

Every experiment is performed on the following cultures:

  • the culture of interest (system studied expressing GFP)
  • the benchmarck used to evaluate R.P.U. (BBa_K173001 measurement part, that is BBa_J23101 with BBa_E0240 downstream)
  • a negative control (generally, BBa_B0033 RBS)

For inducible systems several plots are reported. The first plot is a panel containing 4 subplots, numerated this way:

(1) (2)
(3)

Plot (1) contains growth curves of the cultures, after blank value has been removed. Every curve is calculated averaging on three replicates of the same culture and subtracting the blank for each time sample. Blank is calculated averaging the replicates of blank wells.

Plot (2) shows the logarithm of absorbance in exponential phase of bacterial growth, determined by a visual inspection of log-plots. These values are used to evaluate doubling time and R.P.U..

Plot (3) contains (dGFP/dt)/O.D., the value named S_cell in Kelly J. et al., 2008 procedure for RPU evaluation.

In these plots are reported black veritcal lines that define the range of values used to evaluate RPU. It is important to underline, as explained in next paragraph, that RPU are calculated on cultures at the same O.D. level, not at the same time.

The second graphic shows S_cell VS O.D.. This plot allows the conparison of S_cell values between different cultures, that are supposed to reach the same level of growth not at the same time, but at the same O.D. value.

The third graphic shows the induction curve. The RPU value is calculated on S_cell values corresponding to O.D. values in exponential phase (typically, from 0.05 to 0.16). The curve is obtained averaging in time S_cell values corresponding to exponential phase.

Error bars rapresent the minimum and maximum value of R.P.U. belonging to the range of O.D. in exponential phase.

Materials
  • Long term glycerol stocks were stored at -80°C with a final glycerol concentration of 20%
  • Antibiotics were: Ampicillin (Amp) 100 ug/ml. It was stored at -20°C in 1000x stocks. Amp was dissolved in water.
  • LB medium was prepare with: 1% NaCl, 1% bactotryptone, 0.5% yeast extract. The medium was not buffered with NaOH.

2009 VCU iGEM Team (NEB10beta)

2009 VCU iGEM Anderson promoter comparison.png

The 2009 Virginia Commonwealth University iGEM team characterized select promoters from the Anderson library by measuring fluorescence of a downstream RBS and RFP coding sequence using flow cytometry. These results are a preliminary indication that the performance of these parts may be dependent on cell strain and/or downstream parts. Additional measurements need to be made to verify the reproducibility of these results. mRNA levels were also measured using quantitative rtPCR, shown below. Surprisingly, RNA levels were found to be inversely related to RFP fluorescence.

2009 VCU iGEM Anderson promoter with RNA measurements.png

User Reviews

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iGEM-Team Goettingen 2012

Characterization experiment by qrtPCR on BBa_J23100, BBa_J23104, BBa_J23105, BBa_J23106, BBa_J23109, BBa_J23112, BBa_J23113, BBa_J23114 by iGEM Team Göttingen (by C. Krüger and J. Kampf)

Description

We used quantitative real-time PCR as a powerful tool for quantification of gene expression. We used this method to examine the expression rate of the Tar receptor gene under control of promoters from the Anderson family of the parts registry. The BioBricks (K777001-K777008) we used for this experiment can be found here.

The reported activities of these promoters are given as the relative fluorescence of these plasmids in strain TG1 [1]. Promoter constructs were cloned into the vector pSB1C3 and expressed in E.coli BL21DE3 grown in LB-media (lysogeny broth). The measurements were performed for each construct and reference as a triplet. Additionally, we included H2O as negative control to predict possible contamination. For the evaluation of our results, the 2–ΔΔCT (Livak) method was applied. We used the weakest promoter with the lowest expression rate as calibrator for the calculations and as reference the housekeeping gene rrsD of E.coli. You can find detailed information of the qrtPCR approach here.


Results & Discussion
Comparison of relative expression rates of constitutive promoters by qrtPCR and relative fluorescence (see parts registry,Anderson family). The blue bar indicates the measured expression rates for our constructs (J23100, J23104, J23105, J23106, J23109, J23112, J23113, J23114) and the red ones those for the literature values represented in the “parts registry”. The measurements are illustrated in a logarithmic application. The standard variation was calculated for our measured values (black error bar).

As mentioned before, both datasets were collected by methods which produce data at different points after the gene expression. Quantitative real time PCR measures the amount of expressed mRNA while relative fluorescence measurements quantify on protein level. In perspective of stability and half-life periods of mRNA and proteins or due to protein modification, it is comprehensive to obtain varying data-sets and expression rates. Another problem that occurred during our quantitative real-time measurements was the deviation in some of biological replicates. This problem was also observed in another group’s experiments (Kelly et al., 2009). They mentioned variations across experimental conditions in the absolute activity of the BioBricks. To reduce variation in promoter activity, they measured the activity of promoters relative to BBa_J23101. Furthermore, the iGEM team of Groningen which participated in 2009 also measured the relative fluorescence of TG1 strain with the promoters J23100, J23109 and J23106 via Relative Promoter Units (RPUs). Their values indicated the comparable tendency to our documented values.
For a more detailed description of our results click here.



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Wisconsin-Madison 2010

This constitutive promoter works very well. However, using it for molcular cloning is difficult. The level of expression acheived by J23100 caused our cells to grow slowly. After transformations we picked smaller colonies to get the best screens, and liquid cultures took an extra 4-6 hours to reach a decent plasmid prep OD. For future users, we recommend using it only at the end of your molecular cloning process to avoid the problems that arise from additional cellular stresses.

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iGEM Groningen 2009

We used a number of the constitutive promoter family members for testing our biobricks. The constitutive promoters show the expected level of fluorescence when transformed into E. coli TOP10 cells. Placing parts behind the promoters turned out to be relatively straight forward. We used this part in combination with several biobricks for building our constructs e.g. BBa_I750016 was placed behind the promoters.

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UNIPV-Pavia iGEM 2010

The BBa_J23100, BBa_J23101, BBa_J23105, BBa_J23106, BBa_J23110, BBa_J23114, BBa_J23116, BBa_J23118 were charcterized in LB and M9 supplemented with glycerol (0.4%) growth media in high copy and low copy vectors in E. coli TOP10 (BBa_V1009).

RPU and doubling time were characterized for all of them, according to the protocols reported below.

The following measurement systems were used for high copy plasmids:

In order to build low copy plasmid measurement systems, the EcoRI-PstI fragment (J231xx-RFP) of each BBa_J61002-BBa_J231xx was assembled into pSB4C5 vector. This fragment contains the constitutive promoter of interest upstream a RBS-RFP-TT expression system.

The following measurement parts were used for low copy plasmids:


The RPU values and doubling times are here reported:

Figure 5 - R.P.U. of the studied promoters from Anderson promoters' collection, LB medium and high copy plasmid (BBa_J61002)
Figure 6 - R.P.U. of the studied promoters from Anderson promoters' collection, M9 medium and high copy plasmid (BBa_J61002)
Figure 7 - R.P.U. of the studied promoters from Anderson promoters' collection, M9 medium and low copy plasmid (pSB4C5). These plasmids were constructed by assembling the EcoRI-PstI fragment of BBa_J61002-BBa_J231xx in pSB4C5 vector, in order to transfer the promoter and the RBS-RFP-TT expression construct from BBa_J61002 to pSB4C5.

The error bars represent the standard deviation for three dfferent wells in the same experiment. Doubling times were evaluated for the described cultures (HC stands for High Copy and LC stands for Low Copy):

Promoter doubling time [minutes]
LB in HC plasmid M9 in HC plasmid M9 in LC plasmid
BBa_J23100 33.75
±
1.34
82.53
±
2.45
86.11
±
4.45
BBa_J23101 35.93
±
0.62
82.68
±
1.84
86.42
±
1.91
BBa_J23105 29.86
±
0.33
63.09
±
7.08
85.00
±
5.13
BBa_J23106 29.17
±
0.96
68.11
±
4.25
88.71
±
0.90
BBa_J23110 31.28
±
0.42
67.52
±
5.87
76.15
±
2.16
BBa_J23114 28.97
±
0.49
59.44
±
5.20
80.12
±
0.95
BBa_J23116 28.14
±
0.25
72.74
±
0.37
81.68
±
3.08
BBa_J23118 32.84
±
0.31
73.64
±
2.41
89.86
±
2.93

It was not possible to evaluate promoters activities in low copy number plasmids in LB because the RFP activity was too weak and not distinguishable from the background.

Discussion: we observed that the ranking previously documented in the Registry is not valid in all the tested conditions, even if a general agreement can be observed. As an example, BBa_J23110 in high copy plasmid is stronger than BBa_J23118, in contrast with the ranking reported in the Registry.

Microplate reader experiments for constitutive promoters (R.P.U. evaluation)

  • 8 ul of long term storage glycerol stock were inoculated in 5 ml of LB or M9 + suitable antibiotic in a 15 ml falcon tube and incubated at 37°C, 220 rpm for about 16 hours.
  • The grown cultures were then diluted 1:100 in 5 ml of LB or M9 supplemented medium and incubated in the same conditions as before for about 4 hours.
  • These new cultures were diluted to an O.D.600 of 0.02 (measured with a TECAN F200 microplate reader on a 200 ul of volume per well; it is not equivalent to the 1 cm pathlength cuvette) in 2 ml (wanted final volume) LB or M9 + suitable antibiotic. In order to have the cultures at the desired O.D.600 (O.D._wanted=0.02), the following dilution was performed:
UNIPV Pavia OD600 dil.png
  • These new dilutions were aliquoted in a flat-bottom 96-well microplate, avoiding to perform dynamic experiments in the microplate frame (in order to prevent evaporation effects in the frame). All the wells were filled with a 200 ul volume.
  • The microplate was incubated in the Tecan Infinite F200 microplate reader and fluorescence and absorbance were measured with this automatic protocol:
    • 37°C constant for all the experiment;
    • sampling time of 5 minutes;
    • fluorescence gain of 50 or 70;
    • O.D. filter was 600 nm;
    • GFP filters were 485nm (ex) / 540nm (em);
    • RFP filters were 535nm (ex) / 620nm (em);
    • 15 seconds of linear shaking (3mm amplitude) followed by 10 seconds of waiting before the measurements in order to make a homogeneous culture.
    • Experiment duration time: about 6 hours.


Data analysis for RPU evaluation

The RPUs are standard units proposed by Kelly J. et al., 2009, in which the relative transcriptional strength of a promoter can be measured using a reference standard.

RPUs have been computed as:

UNIPV Pavia RPU formula.png

in which:

  • phi is the promoter of interest and J23101 is the reference standard promoter (taken from the Anderson Promoter Collection);
  • F is the blanked fluorescence of the culture, computed by subtracting for each time sample the fluorescence value of a negative control (a non-fluorescent culture). In our experiments, the TOP10 cells bearing BBa_B0032 or BBa_B0033 were usually used because they are RBSs and do not have expression systems for reporter genes;
  • ASB is the blanked absorbance (O.D.600) of the culture, computed as described in "Preliminary remarks" section.

RPU measurement has the following advantages (under suitable conditions)

  • it is proportional to PoPS (Polymerase Per Second), a very important parameter that expresses the transcription rate of a promoter;
  • it uses a reference standard and so measurements can be compared between different laboratories.

The hypotheses on which RPU theory is based can be found in Kelly J. et al., 2008, as well as all the mathematical steps. From our point of view, the main hypotheses that have to be satisfied are the following:

  • the reporter protein must have a half life higher than the experiment duration (we use GFPmut3 - BBa_E0040 -, which has an estimated half life of at least 24 hours, or an engineered RFP - BBa_E1010, for which the half life has not been measured, but is qualitatively comparable with the GFP's);
  • strain, plasmid copy number, antibiotic, growth medium, growth conditions, protein generator assembled downstream of the promoter must be the same in the promoter of interest and in J23101 reference standard.
  • steady state must be valid, so (dF/dt)/ASB (proportional to the GFP synthesis rate per cell) must be constant.

In order to compute the RPUs, the Scell signals ((dGFP/dt)/ASB)) of the promoter of interest and of the reference J23101 were averaged in the time interval corresponding to the exponential growth phase. The boundaries of exponential phase were identified with a visual inspection of the linear phase of the logarithmic growth curve.


  • Stanford BIOE44 Fall 2018

We used a constitutive promoter as a component part of our experimental plasmid. However, we used the constitutive promoter as a positive control by placing it upstream of GFP. We present our experience here.

In order to ensure that this constitutive promoter works and does not itself exhibit a confounding glucose-concentration dependence, we designed a simple positive-control plasmid consisting of a constitutive promoter upstream of GFP in the promoterless pColi backbone.

We resuspended bacteria with each plasmid in 10 mL of LB broth overnight. For the plasmid, we measured fluorescence over glucose concentrations ranging from 17.78 mM to 0.03 mM using two-fold dilutions and 0 mM to characterize a dynamic range.

It exhibits a relatively constant fluorescence level across glucose concentrations, which is consistent with expected constitutive expression.

"Time-averaged dose-response curves from initial time point to three hours with sampling every 15 minutes. Glucose concentrations ranged from 0.035 mM to 17.78 mM with each concentration doubling the previous. Normed fluorescence levels at a glucose concentration of 0 mM (not shown on semi-log plot) fell below the error bars of the fluorescence level for 0.035 mM for Plasmid E. Mean ± standard error shown for each point."


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