Heterologous expression

Heterologous expression refers to the expression of a gene or part of a gene in a host organism, which does not naturally have this gene or gene fragment. Insertion of the gene in the heterologous host is performed by recombinant DNA technology. The gene is inserted to this host, it can be integrated into the host DNA causing permanent expression, or not integrated causing transient expression of this gene. Heterologous expression can be done in many type of host organisms. The host organism can be a bacterium, yeast, mammalian cell, or plant cell. This host is called the "expression system".