Cloning of the α-enolase gene
1-6-1 Isolation of the enolase gene
The enolase gene has to be isolated from a known source; for example, a known microbial source[16].
1-6-2 PCR amplification of the gene
The gene has to be amplified by PCR prior to the design of the primers. The forward primer is to be exactly the same as that of the DNA sequence of the gene [20-25 bps]. The reverse primer is to be designed in such a way that the sequence has to be exactly the opposite of the coding strand of DNA. Once the primers are designed ,they are used in PCR cycle with denaturing temperature and time of 94°C for 1 minute, annealing temperature and time of 50°C for 30 seconds, and extension temperatures and times of 72°C for 3 minutes. The Primers should have same melting temperature. The primer annealing temperature should be 2 degree celsius less than the melting temperature. The annealing temperature should not be lower than the melting temperature, since it will result in non-specific binding and if the temperature reaches a level that is slightly high, then there will be no binding at all [17].
1-6-3 Restriction digestion of the gene and the vector
The restriction digestion of the gene and the vector has to be carried out. Here the vector to be used is the pET28a vector. There are several restriction sites present in the vector, so the restriction sites which are present in the gene towards the end are chosen carefully and the sites which are in the middle are discarded. The same restriction sites are also chosen in the vector. Then, both the vector and the gene insert are incubated with the respective restriction enzymes for the desired time. After the restriction digestion, the vector and the gene so digested are run in the agars gel electrophoresis for purification purposes. The band showing the corresponding vector band and the gene band are cut and then eluted with the help of the gel extraction kit[18].
1-6-4 Ligation of the gene and vector
The gene and the vector are legated with the help of the lipase enzyme. Thereafter, the entire gene vector construct is again visualized in the agars gel by the help of the electrophoresis[19].
1-6-5 Transformation of the gene–vector construct into the competent cells
A suitable host is used for transformation of the gene vector construct .The host can be E.coli BL 21 cells or NEB 5 α or DH5 α cells. The cells are made competent with the help of the calcium chloride treatment. The vector gene construct also has an antibiotic selection marker gene in it. Then the cells are grown in the agar plate containing the antibiotic that is present as the selection marker in the vector construct, which will yield two types of colonies; namely, the cells which have the vector and the cells which have both vector and the gene itself. The cells can be screened through the process of the blue white screening method in which the cells are, made to grow on the plate containing a substrate known as X-gal. The cells which have the recombinant plasmids are grown into white colonies, and the cells containing the non-recombinant plasmids are grown into blue colonies. Sometimes the screening procedure of the blue white screening method is not a decisive method. So for that reason, the procedure which is followed is colony PCR. In colony PCR, the cell colonies are picked and subjected to the PCR with the same conditions of the amplification and also the same primers previously designed. The colonies having the recombinant plasmids are amplified and will show the positive band on the gel upon being electrophoreses[20].
1-6-6 Isolation of the recombinant plasmid
The recombinant plasmid is isolated through the alkaline lyses method. Alkaline lyses is the protocol used to isolate plasmid DNA by breaking the cells open. Here the cell containing the plasmid of interest is first grown and is lyses with an Alkaline lyses buffer consisting of sodium doddery sulfate (SDS) and a strong base of sodium hydroxide. The phospholipids belayed of the membrane is cleaved by the detergent and the alkali denatures the proteins. The plasmid is isolated and purified by the addition of phenol/chloroform which denatures DNA [21].
1-6-7 Expression of the gene
The recombinant plasmid is inserted into the component cells previously prepared and transformed. Then the cells are grown in a suitable media till the O.D. of 0.1. After that the induction is done with that of the 1mM IPTG final concentration. Then the total cells are boiled and the protein comes out. The protein so obtained is subjected to run in the SDS PAGE for expression. Usually the protein from the cells having an OD of 0.5 is taken for the checking of the expression of the gene. Here IPTG is used, since it cannot be used by the E.coli cells for growth moreover, IPTG is a structural analogue of the lactose, so lac operand will be active which is present in the plasmid[22]. Reasons for using the pET28a plasmid .The plasmid pET28a has T7 promoter, which is a very strong promoter ,due to which the production of RNA will be more which leads to more protein production. The presence of the lac operand inducible expression can happen as a result of the use of IPTG in place of the lactose[23].