Editing Gene expression (section)

==Expression system==
[[Image:Tet-ON inducible transgene expression cells.svg|thumbnail|500px|Tet-ON inducible shRNA system]]
{{main|Protein production (biotechnology)}}

An expression system is a system specifically designed for the production of a gene product of choice. This is normally a protein although may also be RNA, such as [[tRNA]] or a [[ribozyme]]. An expression system consists of a gene, normally encoded by [[DNA]], and the [[molecular machinery]] required to [[Transcription (genetics)|transcribe]] the DNA into [[mRNA]] and [[translate]] the mRNA into [[protein]] using the reagents provided. In the broadest sense this includes every living cell but the term is more normally used to refer to expression as a laboratory tool. An expression system is therefore often artificial in some manner. Expression systems are, however, a fundamentally natural process. Viruses are an excellent example where they replicate by using the host cell as an expression system for the viral proteins and genome.

===Inducible expression===
[[Doxycycline]] is also used in "Tet-on" and "Tet-off" [[tetracycline controlled transcriptional activation]] to regulate [[transgene]] expression in organisms and [[cell culture]]s.

===In nature===
In addition to these biological tools, certain naturally observed configurations of DNA (genes, promoters, enhancers, repressors) and the associated machinery itself are referred to as an expression system. This term is normally used in the case where a gene or set of genes is switched on under well defined conditions, for example, the simple repressor switch expression system in [[Lambda phage]] and the [[lac operator]] system in bacteria. Several natural expression systems are directly used or modified and used for artificial expression systems such as the [[Tetracycline controlled transcriptional activation|Tet-on and Tet-off]] expression system.