Heterologous expression as a tool for gene identification and analysis.

These days, genome research mainly concerns the accumulation of sequence data and their theoretical interpretation based on analogies to known genes, proteins and structures. However, a final identification of gene function can only be verified by experimental data. One step in this process is the expression of the isolated gene in pro- and eukaryotes. In this article we will review some of the basic features of expression in Escherichia coli and mammalian cells that are relevant to the design of expression experiments. Emphasis is put on the first instance of attaining a high enough level of expression in order to be able to detect the cellular effects or to isolate the product of the transferred gene.