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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]
One known example of these transport proteins is the melibiose, or melB, carrier protein derived from the melB gene of E. coli. [3] This strain of beta-galactoside permease is known it transport melibiose and other galactosides across the cell membrane using hydrogen, sodium, or lithium ions in cotransport. [4]
The enzyme's role in the classical E.coli lac operon remains unclear. [1] [3] However, the enzyme's cellular role may be to detoxify non-metabolizable pyranosides by acetylating them and preventing their reentry into the cell. [1] [4]
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. The absence of lactose permease leads to the inability of lactose to enter the cell for further metabolic processes.
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.
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 repressor (LacI) is a DNA-binding protein that inhibits the expression of genes coding for proteins involved in the metabolism of lactose in bacteria. These genes are repressed when lactose is not available to the cell, ensuring that the bacterium only invests energy in the production of machinery necessary for uptake and utilization of ...
The first natural gene circuit studied in detail was the lac operon. In studies of diauxic growth of E. coli on two-sugar media, Jacques Monod and Francois Jacob discovered that E.coli preferentially consumes the more easily processed glucose before switching to lactose metabolism. They discovered that the mechanism that controlled the ...