Genetic studies including the quest, cloning and expression of genes encoding proteins responsible for various vital physiological processes and beneficial characteristics of economic perspective have made the biotechnology research progressively auspicious. Due to its great zootechnical and industrial importance somatotropin gene have been cloned from various animal species. Current study was designed to clone mature GH cDNA of a sheep breed Kajli and carry out over expression studies of cloned GH cDNA in a suitable prokaryotic expression system. Sheep GH cDNA was cloned in T/A vector with signal peptide and confirmed by nested PCR and restriction digestion. The gene was then ligated in pLEX expression vector and restricted plasmids showed a fragment insert of ~600bps. Restriction analysis confirmed positive clones, were induced for protein expression analysis. The pET vectors have an IPTG inducible strong T7 promoter and E. coli expression strain of BL21 (DE3) pLysS contains DNA fragment from T7 phage which harbors RNA polymerase. Therefore, for expressing recombinant proteins, cells were induced with various IPTG concentrations to optimize expression levels. Cells were induced with different IPTG concentrations (0.1 mM to 0.8 mM) followed by SDS-PAGE. Results indicated maximum expression level of oGH at 5 hrs after induction of cells with 0.3 mM IPTG concentration with a molecular weight of 22 kDa. As for as cellular localization of protein is concerned accumulation of expressed oGH is observed in inclusion bodies. The successful expression of the cloned GH cDNA of sheep confirms the functional viability of the clone.

Key words: Cloning; over expression; cDNA; ovine somatotropin; Kajli sheep, prokaryotic system