Guidelines for Choosing a Heterologous Expression System

A heterologous gene expression system is chosen with regard to both its characteristics and the anticipated application of the expressed protein. Often, both economic and production issues play a major role in choosing a particular expression system. An ideal system provides both low cost and high production capacity. 

In the context of viral assembly, biological activity refers primarily to the ability of the assembled material to perform some of the functions associated with native virions or their components. This includes the 

Before embarking on a particular expression strategy it is useful to have some information regarding the hands-on time required before the first results can be obtained. The fastest turnaround times are achieved with cell lysates, such as the reticulocyte and wheat germ lysates, which only need to be primed with in vitro synthesized RNA (or DNA in the case of a coupled transcription/translation system). These systems potentially provide answers within a few hours but are rarely used because of the small quantities that they yield. Plasmid-based systems used for expression in E. coli, yeast, and in combination with the vaccinia-T7 vector system are relatively fast as well. These strategies require subcloning of the gene(s) of interest into a plasmid vector, which is then transfected into the 

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