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The lactose operon (lac operon) is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria.Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of β-galactosidase. [1]
The lac operon is used in the biotechnology industry for production of recombinant proteins for therapeutic use. The gene or genes for producing an exogenous protein are placed on a plasmid under the control of the lac promoter. Initially the cells are grown in a medium that does not contain lactose or other sugars, so the new genes are not ...
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The lac operon of the model bacterium Escherichia coli was the first operon to be discovered and provides a typical example of operon function. It consists of three adjacent structural genes, a promoter, a terminator, and an operator. The lac operon is regulated by several factors including the availability of glucose and lactose.
As well as genetic resistance the SOS response can also promote phenotypic resistance. Here, the genome is preserved whilst other non-genetic factors are altered to enable the bacteria to survive. The SOS dependent tisB-istR toxin-antitoxin system has, for example, been linked to DNA damage-dependent persister cell induction. [12]
The tac promoter finds various applications. The tac promoter/operator (dubbed PTAC) is one of the most widely used expression systems.Ptac is a strong hybrid promoter composed of the –35 region of the trp promoter and the –10 region of the lacUV5 promoter/operator.
When referring to a promoter some authors actually mean promoter + operator; i.e., the lac promoter is IPTG inducible, meaning that besides the lac promoter, the lac operon is also present. If the lac operator were not present the IPTG would not have an inducible effect. [citation needed] Another example is the Tac-Promoter system (Ptac ...
Lactose permease is a membrane protein which is a member of the major facilitator superfamily.Lactose permease can be classified as a symporter, which uses the proton gradient towards the cell to transport β-galactosides such as lactose in the same direction into the cell.