Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, and ultimately affect a phenotype. These products are often proteins, but in non-protein-coding genes such as transfer RNA (tRNA) and small nuclear RNA (snRNA), the product is a functional non-coding RNA. The process of gene expression is used by all known life—eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea), and utilized by viruses—to generate the macromolecular machinery for life.

For vocabulary, see Glossary of gene expression terms. For a non-technical introduction to the topic, see Introduction to genetics.

In genetics, gene expression is the most fundamental level at which the genotype gives rise to the phenotype, i.e. observable trait. The genetic information stored in DNA represents the genotype, whereas the phenotype results from the "interpretation" of that information. Such phenotypes are often displayed by the synthesis of proteins that control the organism's structure and development, or that act as enzymes catalyzing specific metabolic pathways.

All steps in the gene expression process may be modulated (regulated), including the transcription, RNA splicing, translation, and post-translational modification of a protein. Regulation of gene expression gives control over the timing, location, and amount of a given gene product (protein or ncRNA) present in a cell and can have a profound effect on the cellular structure and function. Regulation of gene expression is the basis for cellular differentiation, development, morphogenesis and the versatility and adaptability of any organism. Gene regulation may therefore serve as a substrate for evolutionary change.

A constitutive gene is a gene that is transcribed continually as opposed to a facultative gene, which is only transcribed when needed.

A is a gene that is required to maintain basic cellular function and so is typically expressed in all cell types of an organism. Examples include actin, GAPDH and ubiquitin. Some housekeeping genes are transcribed at a relatively constant rate and these genes can be used as a reference point in experiments to measure the expression rates of other genes.

housekeeping gene

A facultative gene is a gene only transcribed when needed as opposed to a constitutive gene.

An inducible gene is a gene whose expression is either responsive to environmental change or dependent on the position in the cell cycle.

Identify viral infection of a cell ( expression).

viral protein

Determine an individual's susceptibility to (oncogene expression).

cancer

Find if a bacterium is resistant to (beta-lactamase expression).

penicillin

evaluates a panel of genes to help understand the fundamental mechanism of a cell. This is increasingly used in cancer therapy to target specific chemotherapy. (See RNA-Seq and DNA_microarray for details.)

Gene expression profiling

Reporter gene

SAGE

The following experimental techniques are used to measure gene expression and are listed in roughly chronological order, starting with the older, more established technologies. They are divided into two groups based on their degree of multiplexity.

(GEO) at NCBI^[140]

Gene expression omnibus

at the EBI

Expression Atlas

Bgee at the SIB Swiss Institute of Bioinformatics

Bgee

Mouse at the Jackson Laboratory

Gene Expression Database

: a database of experimentally validated transcription factor-binding sites in Bacteria.^[141]

CollecTF

COLOMBOS: collection of bacterial expression compendia.

[142]

: microbial Affymetrix data^[143]