Part:BBa_K2596001

PcpcB from Synechococcus elongatus PCC7942

PcpcB is a constitutive promoter from cyanobacteria Synechococcus elongatus PCC 7942.

Usage and Biology

cpcB codes for phycocyanin, a phycobiliprotein complex, and works to harvest light energy before transmitting it to the chlorophylls. The promoter is a strong promoter but also demonstrates expression patterns following circadian oscillations. Studies have found that Pcpc can also be used in E. coli.

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
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]

PcpcB1A1 features two promoter sequences within the promoter, both of which were included in the BioBrick. For this promoter, derived from Synechococcus elongatus PCC 7942, we kept about 100 bp of upstream and downstream regions, the latter of which was cropped immediately before the ATG start codon. Studies have found that Pcpc can also be used in E. coli.

Luciferase Assays

Figure 1. Daytime and nighttime standard expression tests for the constitutive promoters cpc and cpc-560.

Figure 2. Daytime Standard Expression of luxAB for the constitutive promoters cpc and cpc-560, ferrous ion repressible idiA, and high light inducible psbA2 promoters

Figure 3. High light exposure Standard Expression tests for the constitutive promoters cpc and cpc-560, ferrous ion repressible idiA, and high light inducible psbA2 promoters

Experimental Methods:

In order to test the expression of our promoters, cpc (BBa_K2596001), cpc560 (BBa_K2596006), idiA (BBa_K2596004), psbA2 (BBa_K2596003), which were incorporated into Dr. Susan Golden’s vector pAM1414 using Gibson assembly, we conducted luciferase experiments. Following Dr. Golden’s procedure, we added 5 µL of decanal to 95 µL of cyanobacteria in each well to induce expression. The decanal acted as a substrate for the bacterial luciferase enzyme, but due to the toxicity, the cells ended up dying, so the data obtained represents the end static expression. For the standard expression experiments for nighttime and daytime, we plated 95 µL of cyanobacteria into a 96 well plate, added 5 µL of decanal, parafilmed the edges and left the plate for 15 minutes before measuring the luminescence in a plate reader. For the psbA2 experiment, we plated 95 µL of cyanobacteria to half of the wells and put them under at least 500 µE of high light in our incubator for 1 hour. Then, we added 95 µL of cyanobacteria not exposed to high light to the other half of the wells and added 5 µL of decanal to all of the wells. Then, we placed the well plate in a plate reader and measured the luminescence.

Results:

After removing outliers from the data set using the 1.5(IQR) rule and conducting unpaired T-tests assuming unequal variance, both cpc and cpc-560 showed significant differences for daytime expression compared to wild type [Figure 1]. Compared to cpc, cpc-560 had a significantly higher expression [Figure 1]. In comparison for day compared to night, cpc did not show any significant difference [Figure 2]. On the other hand, cpc-560 showed a significant difference between daytime and nighttime expression [Figure 2].

After removing outliers from the data set using the 1.5(IQR) rule and conducting unpaired T-tests assuming unequal variance, for daytime expression, compared to all other promoters and the wild type, cpc and cpc-560 had significant differences in expression [Figure 1]. For idiA and psbA2, they only had significant differences compared to cpc and cpc-560, and not to each other [Figure 1]. When exposed to highlight, idiA and psbA2 did not show any expression [Figure 3].