The oldest and most widely used expression systems are cell - based and may be defined as the "combination of an expression vector, its cloned DNA, and the host for the vector that provide a context to allow foreign gene function in a host cell, that is, produce proteins at a high level ''. Overexpression is an abnormally and excessively high level of gene expression which produces a pronounced gene - related phenotype.
protien export from the cell is an example of
gene expression