Gene expression (also protein expression or often simply expression) is the process by which a gene's information is converted into the structures and functions of a cell.
Gene expression is a multi-step process that begins with transcription and translation and is followed by folding, post-translational modification and targeting.
The amount of protein that a cell expresses depends on the tissue, the developmental stage of the organism and the metabolic or physiologic state of the cell.
Indirectly, the expression of particular genes may be assessed with DNA microarray technology, which can provide a rough measure of the cellular concentration of different mRNAs; often thousands at a time. While the name of this type of assessment is actually a misnomer, it is often referred to as expression profiling . (The expression of many genes is known to be regulated after transcription, so an increase in mRNA concentration need not always increase expression.)
Control of expression
Control of gene expression depends various factors including:
The protein encoded for by a gene can be expressed in increased quantity. This can come about by:
- increasing the number of copies of the gene
- increasing the binding strength of the promoter region
Often, the DNA sequence for a protein of interest will be spliced into a plasmid containing the lac promoter and used for transformation of bacteria. Addition of IPTG (a lactose analog) causes the bacteria to produce (express)the protein of interest. It doesn't work with every protein (sometimes yeast do a better job with post-translational modifications), but bacterial expression can sometimes be used to make a lot of protein with minimal fuss, for example for X-ray crystallography or NMR structure determination.
Gene networks and expression
Main article: Gene regulatory network
Genes have sometimes been regarded as nodes in a network, with inputs being proteins such as transcription factors, and outputs being the level of gene expression. The node itself performs a function, these and the operation of these functions have been interpreted as performing a kind information processing within cell and determine cellular behaviour.