With the advent of our ability to clone and express a foreign gene in the h
eterologous host, came a remarkable capability to make almost any protein i
n abundant quantity to be used as therapeutic or diagnostic agents. It quic
kly led to the realization that proteins made in different hosts are differ
ent in many ways, particularly in their post-translation modifications. In
this review a variety of available expression host systems are evaluated fo
r heterologous production of proteins. Factors affecting the stability and
expression of heterologous genes are also discussed, Eventual objective of
producing a desired protein in an economical heterologous host is influence
d by a variety of factors discussed in this review. Subsequent to the produ
ction, stabilization and formulation of proteins will pose significant hurd
les in utilizing the natural biological catalysts and other proteins for th
erapeutic and industrial purposes.