BBa_K2557001

The Peking iGEM 2017 team identified the properties of Bxb1 gp35(BBa_K2243012)in E. coli. We obtained the sequence of this part and requested the plasmid from them. Since our chassis organism is mammalian cell, we optimized the codon and then we identified BBa_K2557001 in detail in HEK 293T cells. Although Bxb1 works well in HEK 293T cells, we did not repeat the activity reported by Peking iGEM 2017 team in E. coli.

Characterization

The results of image B show that the reverse efficiency of Bxb1 recombinase is higher than TP901 recombinase under the same promoter strength and recombinase concentration. However, if the concentration of recombinase is low, there is no significant difference in fluorescence intensity. The results of the image C show that Bxb1 and TP901 recombinases have a threshold property. So, the proportion of fluorescent cells have a jump discontinuity between low concentration and high concentration of recombinase.

Characterization in original part

The Peking iGEM 2017 team identified the properties of Bxb1 gp35(BBa_K2243012)in E. coli. We obtained the sequence of this part and requested the plasmid from them. Since our chassis organism is mammalian cell, we optimized the codon and then we identified BBa_K2557001 in detail in HEK 293T cells. Although Bxb1 works well in HEK 293T cells, we did not repeat the activity reported by Peking iGEM 2017 team in E. coli.

Pronuclear verification of recombinase

Two plasmids with different resistances and origins of replication were used for function verification of the recombinase. One of them is a reporter gene plasmid, which uses the constitutive promoter J23119. The recombination site is located on both sides of the promoter: one side is sfGFP, and the other is mRFP. The other plasmid is a recombinase expression plasmid using PBAD, an inducible promoter, which is induced by arabinose. When the two plasmids were co-transfected into E. coli, the reporter plasmid expressed sfGFP, a kind of green fluorescent protein; when the inducer arabinose was added, the recombinant enzyme was expressed, the promoter was inverted, and the mRFP , a kind of red fluorescent protein, was expressed.

Due to the use of two different resistant plasmids, kana and chloramphenicol, we used a plate containing two resistances of kana and chloramphenicol for screening, grew more colonies, and randomly selected 9 singles. After the colonies, we made colony PCR (Fig. 1) and the results showed that both plasmids were transferred.

The verified E. coli was separately placed in a 1.5 ml centrifuge tube containing antibiotic-containing LB medium, and the culture was grown at 37° C and 200 RPM for 6 hours, and then the culture was aliquoted into two portions, one of which was added with an inducer (10 mM Arabinose). Two cultures were grown for 12 hours at 37°C and 200 RPM, and the mixture was incubated for 1 hour at room temperature prior to testing. Both lasers are used to excite both sfGFP and mRFP.

The result shows no obvious fluorescence. We changed some conditions, such as lowering the temperature, adjusting the rotation speed, adjusting the time, etc. But we still did not get the expected results. We consulted the teacher and the teacher replied that there might be weak fluorescence but our instrument couldn't detect it.