Metabolic load and heterologous gene expression.

The expression of a foreign protein(s) in a recombinant host cell or organism often utilizes a significant amount of the host cell's resources, removing those resources away from host cell metabolism and placing a metabolic load (metabolic drain, metabolic burden) on the host. As a consequence of the imposed metabolic load, the biochemistry and physiology of the host may be dramatically altered. The numerous physiological changes that may occur often lowers the amount of the target foreign protein that is produced and eventually recovered from the recombinant organism. In this review the physiological changes to host cells, the causes of the phenomenon of metabolic load, and several strategies to avoid some of the problems associated with metabolic load are elaborated and discussed.