Transformation of calcium-competent cells was carried out by the procedure detailed below: •The competent bacterial cells were thawed briefly and 200 μL of cells was mixed rapidly with plasmid DNA (10-50 ng) in fresh, sterile microcentrifuge tubes and maintained on ice for 30 min. A negative control with competent cells only (no added DNA) was also included. •Cell membranes were disrupted by subjecting cells to heat-pulse (42 °C) for 90 sec. •After heat shock, cells were incubated on ice for 5 min. •Cells were then mixed with 1 mL LB medium and incubated with shaking at 37 °C for 1 h. •For blue/white screening 40 μL of X-gal solution (20 mg mL-1 in dimethylformamide) and 4 μL of the IPTG (200 mg mL-1) was spread on LB-ampicillin (LB-amp) plates with a sterile glass rod. The plate was allowed to dry for 1h at 37 °C prior to spreading of bacterial cells. •Bacterial cells (100-200 μL) were spread and the plate was incubated at 37 °C for overnight. •White colonies were picked from the plates and suspended into LB-amp broth and cultivated to OD600=0.5

In order to minimize self ligation of vector during cloning experiments, the digested DNA was subsequently treated with calf intestinal phosphatase (CIP) [NEB, UK]. The reaction conditions and amount of CIP were optimized and varied from (0.06-1) unit/picomole DNA termini. The dephosphorylation reaction was carried out in 50 μL reaction as follows. Reaction mixture containing no restriction enzyme was treated as control. Reaction was incubated for 1 h at 37 °C and stopped by heat inactivation at 65 °C for 20 min. 2.5.5. Composition of restriction mixture (50 μL) Linearized Plasmid DNA X μL (1 μg) CIP 1 μL (0.06-1 U μL-1) Reaction buffer (10X) 5.0 μL Distilled water Y μL Total volume 50 μL Linearized and dephosphorylated plasmids from each reaction were purified from low melting agarose gel using gel extraction method according to the manufacturer’s protocol (Qiagen gel extraction kit, Germany). 100 ng DNA from each reaction was then ligated in15 μL reaction volume containing 1.5 μL of 10X ligation buffer (NEB, England) and 0.2 μL of T4 DNA ligase to check the efficiency of self ligation after dephosphoryaltion. The ligation mixture was incubated at 16 °C for overnight and transformed into E. coli DH5αcompetent cells.