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A typical operon. In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. [1] The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product.
Structure of the trp operon. The trp operon is a group of genes that are transcribed together, encoding the enzymes that produce the amino acid tryptophan in bacteria. The trp operon was first characterized in Escherichia coli, and it has since been discovered in many other bacteria. [1]
Having multiple ORFs on a single mRNA is only possible in prokaryotes because their transcription and translation take place at the same time and in the same subcellular location. [23] [28] The operator sequence next to the promoter is the main regulatory element in prokaryotes. Repressor proteins bound to the operator sequence physically ...
Changes in the regulation of gene networks are a common mechanism for prokaryotic evolution.An example of the effects of different regulatory environments for homologous proteins is the DNA-binding protein OmpR, which is involved in response to osmotic stress in E. coli but is involved in response to acidic environments in the close relative Salmonella Typhimurium.
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]
For amino acid biosynthesis operons, these allow the gene expression machinery to sense the abundance of the amino acid produced by the encoded enzymes, and adjust the level of downstream gene expression accordingly: transcription occurring only if the amino acid abundance is low and the demand for the enzymes is therefore high.
The genes of prokaryotes are grouped together based on similar functions into units called operons which consist of a promoter and an operator. The operator is the binding site for the repressor and thus has a function equivalent to the silencer region in Eukaryotic DNA.
The gal operon is a prokaryotic operon, which encodes enzymes necessary for galactose metabolism. [1] Repression of gene expression for this operon works via binding of repressor molecules to two operators. These repressors dimerize, creating a loop in the DNA.