A Dual-Expression Vector Allowing Expression in E. coli and P. pastoris, Including New Modifications

Heterologous gene expression is often treated empirically and a number of host organisms are systematically tested. Early successes in the expression of recombinant proteins were achieved using the well-studied bacterium Escherichia coli (1 ). This prokaryotic expression system is simple to handle, costeffective, and produces large amounts of heterologous proteins (2 ). However, when expressing many different genes, especially eukaryotic genes, this often leads to the production of aggregated and denatured proteins, localized in inclusion bodies, and only a small fraction matures into the desired native form (3 –5 ). Alternatively, eukaryotic expression systems have been developed to obtain more soluble protein, which in addition, may undergo some eukaryotic post-translational modifications. Yeast expression systems, including the methylotrophic yeast Pichia pastoris , have been used over the last few years as powerful expression systems for a number of heterologous genes (6 –10 ). However, both eukaryotic and prokaryotic systems have their advantages and disadvantages. Therefore, choosing a suitable expression system for a particular protein is a compromise, depending primarily on the properties of the protein, the amounts required, and its intended purpose.