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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 an interesting example of how gene expression can be regulated. Viruses, despite having only a few genes, possess mechanisms to regulate their gene expression, typically into an early and late phase, using collinear systems regulated by anti-terminators (lambda phage) or splicing modulators .
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 ...
An example of a cis-acting regulatory sequence is the operator in the lac operon. This DNA sequence is bound by the lac repressor, which, in turn, prevents transcription of the adjacent genes on the same DNA molecule. The lac operator is, thus, considered to "act in cis" on the regulation of the nearby genes.
Monod joined the Pasteur Institute in 1943 and Jacob in 1949. The experimental system ultimately used by Jacob and Monod was a common bacterium, E. coli, but the basic regulatory concept (described in the Lac operon article) that was discovered by Jacob and Monod is fundamental to cellular regulation for all organisms.
The lac operon in the prokaryote E. coli consists of genes that produce enzymes to break down lactose. Its operon is an example of a prokaryotic silencer. The three functional genes in this operon are lacZ, lacY, and lacA. [6] The repressor gene, lacI, will produce the repressor protein LacI which is under allosteric regulation.
It is encoded by the lacY gene in the lac operon. The LacY gene is a component of the lac operon that encodes lactose permease, a protein responsible for breaking down lactose into glucose and galactose, alongside transacetylase and beta galactosidase.
Taking advantage of an operon fusion placing the lac operon (responsible for producing beta-galactosidase, a protein which degrades lactose) under the control of an SOS-related protein, a simple colorimetric assay for genotoxicity is possible.