Plasmid DNA. pEGFP-c3 (Clontech), which encodes for an enhanced green fluorescence protein (GFP) under a CMV promoter, was amplifien in Escherichia coli (DH5a) and purifien using Qiagen Midi Prep plasmid purification protocol (Qiagen, Germany). Purity of the plasmild was checked by electrophoresis on 1.0% agarose gel. Concentration of the DNA was estimated spectroscopically by measuring the absorption at 260 nm and confirmed by gel electrophoresis.The plasmid preparations showing a value of OD260/OD280>1.8 were used.