The PCRs were normally performed using Taqpolymerasefrom Roche or Fermentas. Approximately 1-5ng of plasmid or 5-100ng of chromosomal DNA was used as a template in a50μlreaction volume containing 200μM of each dNTP, 20pM each of the forward and reverse primers and 1 unit of Taq DNA polymerase. For colony PCR E. coli cells from a freshly grown plate were resuspended in 10μl of sterile Milli-Q water to get a cell suspension and this was used as a template in a PCR reaction at a final volume of 50μl. The samples were typically subjected to 30 cycles of amplification with the following general conditions: Initial denaturation 95ºC5minutes Denaturation 95ºC 1 minute Annealing 55ºC 1 minute Extension 72ºC 1 minute/kb of DNA template to be amplified Final extension 72ºC 10 minutes

Polymerase Chain Reaction (PCR)

Molecular techniques

Restriction enzyme digestion and analysis

desired temperaturefor 45 minutes and plated on an appropriate selective medium at various dilutions. An aliquot of cell suspension to which plasmid DNA was not added served as a negative control. B. Inoue method i. Preparation of high efficiency competent cells Competent cells for high efficiency transformation were prepared by the method of (Inoueet al., 1990)with few modifications. An overnight culture of the strain (routinely DH5α) was subculturedinto fresh sterile LB broth in 1:100 dilutions and grown at 18ºC to anA600of 0.55. The cells were harvested by centrifugation at 2500rpm for 10 minutes at4ºC. Thesecells wereresuspended in0.4 volumes of INOUE buffer andincubated in ice for 10 minutes. The cells were recovered by centrifugation at 2500rpm at 4ºC for 10 minutes and finally resuspended in 0.01 volume of the same buffer. Sterile DMSO was added to a final concentration of 7%. After incubating for 10 minutes in ice, the cells were aliquoted in 100μl volumes, snap frozen in liquid nitrogen and stored at –80ºC. ii. Transformation protocolFor transformation, the required number of vials wasthawed on ice and the transformation protocol as described for CaCl2method was employed

A. Calcium chloride(CaCl2)method For routine plasmid transformation, following method which is a modification of that described by(Cohenet al.,1972)was used. An overnight culture of recipient strain was subcultured 1:100 in fresh LB medium and grown till mid-exponential phase. The culture was chilled on ice for 20 minutes, and the steps thereafter performed at 4ºC. 10 ml of culture was centrifuged and pelletwas resuspended in 5 ml of 0.1M CaCl2. After 5 minutes of incubation on ice, the cells were again centrifuged and resuspended in 1ml of 0.1M CaCl2. The suspension was incubated onice for 45 minutes. To the 100μl aliquot of the cellsuspension plasmid DNA (20-200ng in less than 10μl volumes) was added, incubated for 30-40 minutes on ice and given a heat shock for 90 seconds at 42ºC. The cultures were rapidly chilled for 1 minute, mixed with 0.9ml of LB broth and incubated at

Transformation