Team:USP-UNESP-Brazil/Plasmid Plug n Play/Results

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We designed two primers, one containing the lox66 and one containing the loxP sequences, these primers amplified the ORF from the kanamycin resistance gene, flanked upstream by the loxP and downstream by the lox66, using PCR. These sites should be recognized by the Cre recombinase (from NEB company), which could circularized our linear PCR product. This is important because we don't want it to be degraded when inserted in the bacteria. This ''In vitro'' assay was a test for a posterior ''In vivo'' assay, where we expect that this process happens inside the ''E. coli'' using a Cre recombinase enzyme expressed by the same bacteria.     
We designed two primers, one containing the lox66 and one containing the loxP sequences, these primers amplified the ORF from the kanamycin resistance gene, flanked upstream by the loxP and downstream by the lox66, using PCR. These sites should be recognized by the Cre recombinase (from NEB company), which could circularized our linear PCR product. This is important because we don't want it to be degraded when inserted in the bacteria. This ''In vitro'' assay was a test for a posterior ''In vivo'' assay, where we expect that this process happens inside the ''E. coli'' using a Cre recombinase enzyme expressed by the same bacteria.     
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Our experiment showed that 5U and 10U of Cre recombinase produced a reduction of linear DNA (Kanamycin resistance gene flanked with loxP and lox66) when compare to 1U of Cre recombinase and to the control DNA (No Cre recombinase added), as is showed in the figure A. It was also observed an increase of the DNA plasmid form (upper band at 2 Kb), as is showed in figure B. We also used a control DNA substrate supplied in the NEB recombinase kit. The same amount of PCR-product was applied to each lane (260 ng).  
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Our experiment showed that 5U and 10U of Cre recombinase reduced the linear DNA (Kanamycin resistance gene flanked with loxP and lox66) amount when compare to 1U of Cre recombinase and to the control DNA (No Cre recombinase added), as is showed in the figure A. It was also observed an increase of the DNA plasmid form (upper band at 2 Kb), as is showed in figure B. We also used a control DNA substrate supplied in the NEB recombinase kit. The same amount of PCR-product was applied to each lane (260 ng).  
The conclusion was that we can use this loxP-lox66 mechanism in our design and we will need at least 5U of Cre recombinase for any ''in vitro'' experiment.  
The conclusion was that we can use this loxP-lox66 mechanism in our design and we will need at least 5U of Cre recombinase for any ''in vitro'' experiment.  
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We transformed the electrocompetent Plug&Play Machine cells with a gradient of our purified PCR-product (kanamycin resistance gene flanked by a loxP and a lox66): 10 ng, 100 ng and 1000 ng. These concentrations were chosen using the mathematical model that the group already had developed. After transformation, the cells (50 ul) were left for 40 min in 1 mL LB medium without antibiotic, for recovering from the transformation stress.  
We transformed the electrocompetent Plug&Play Machine cells with a gradient of our purified PCR-product (kanamycin resistance gene flanked by a loxP and a lox66): 10 ng, 100 ng and 1000 ng. These concentrations were chosen using the mathematical model that the group already had developed. After transformation, the cells (50 ul) were left for 40 min in 1 mL LB medium without antibiotic, for recovering from the transformation stress.  
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The LB medium (1 mL) where the bacteria were recovering was equally divided in three LB solid plates. One plate had ampicillin (100 ug/mL) and IPTG (1 mM), the second had kanamycin (50 ug/mL) and IPTG (1 mM) and the last one had both antibiotics (ampicillin (100 ug/mL) and kanamycin (50 ug/mL)) and IPTG (1 mM). The plates were left in incubation for 15 h at 37°C. As a control, the pET15b (25 ng) commercial plasmid was used for a independent transformation of the ''E. coli'' (Bl21(DE3)) lineage and plated in the same three kind of plates. The pET15b plasmid has a gene that confers resistance to ampicillin.   
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The LB medium (1 mL) where the bacteria were recovering was equally divided in three LB solid plates. One plate had ampicillin (100 ug/mL) and IPTG (1 mM), the second had kanamycin (50 ug/mL) and IPTG (1 mM) and the last one had both antibiotics (ampicillin (100 ug/mL) and kanamycin (50 ug/mL)) and IPTG (1 mM). The plates were left in incubation for 15 h at 37°C. As a control, the pET15b (25 ng) commercial plasmid was used for an independent transformation of the ''E. coli'' (Bl21(DE3)) lineage and plated in the same three kind of plates. The pET15b plasmid has a gene that confers resistance to ampicillin.   
Our control worked as expected, the bacteria grew in the ampicillin plate but no in the kanamycin plate nor the plate with both antibiotics (Fig. 1). For the bacteria transformed with 10 ng of PCR-product, we found growth just in the ampicillin plate, which means that the bacteria had the Plug&Play plasmid, but no recombination had happened (Fig. 2).  
Our control worked as expected, the bacteria grew in the ampicillin plate but no in the kanamycin plate nor the plate with both antibiotics (Fig. 1). For the bacteria transformed with 10 ng of PCR-product, we found growth just in the ampicillin plate, which means that the bacteria had the Plug&Play plasmid, but no recombination had happened (Fig. 2).  
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For the bacteria transformed with 100 ng and 1000 ng of PCR-products we found colonies in the three plates. Find colonies in the plate with both antibiotics (Fig. 3 and Fig. 4) strongly suggest that the bacteria had a Plug&Play plasmid where the recombination of the PCR-product into the lox71 site occurred. We counted the number of colonies in both plates: 36 colonies grew in the plate of bacteria transformed with 10 ng of PCR-product and 611 for the plate of bacteria transformed with 100 ng of PCR-product.  
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For the bacteria transformed with 100 ng and 1000 ng of PCR-products we found colonies in the three plates. Find colonies in the plate with both antibiotics (Fig. 3 and Fig. 4) strongly suggest that the bacteria had a Plug&Play plasmid where occurred the PCR-product recombination into the lox71 site. We counted the number of colonies in both plates: 36 colonies grew in the plate of bacteria transformed with 10 ng of PCR-product and 611 for the plate of bacteria transformed with 100 ng of PCR-product.  
The kanamycin gene that we used cant express or replicate without being in the plasmid, it has no promoter or replication site, we cloned just the ORF of the gene. This gene will be expressed as long as IPTG is present in the culture medium.   
The kanamycin gene that we used cant express or replicate without being in the plasmid, it has no promoter or replication site, we cloned just the ORF of the gene. This gene will be expressed as long as IPTG is present in the culture medium.   

Revision as of 02:53, 27 September 2012

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