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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.
The distance between each gene in the gene cluster can vary. The DNA found between each repeated gene in the gene cluster is non-conserved. [10] Portions of the DNA sequence of a gene is found to be identical in genes contained in a gene cluster. [5] Gene conversion is the only method in which gene clusters may become homogenized. Although the ...
For example, an operon is a stretch of DNA that is transcribed to create a contiguous segment of RNA, but contains more than one cistron / gene. The operon is said to be polycistronic, whereas ordinary genes are said to be monocistronic.
The maltose operon is an example of a positive control of transcription. [1] When maltose is not present in E. coli, no transcription of the maltose genes will occur, and there is no maltose to bind to the maltose activator protein.
Mechanism of transcriptional attenuation of the trp operon. An example is the trp gene in bacteria. When there is a high level of tryptophan in the region, it is inefficient for the bacterium to synthesize more. When the RNA polymerase binds and transcribes the trp gene, the ribosome will start translating. (This differs from eukaryotic cells ...
This selfish operon model suggests that individual genes were grouped together by vertical en horizontal transfer and were preserved as a single unit because that was beneficial for the genes, not per se for the organism. This model predicts that the gene clusters must have conserved between species.
For EST data, clustering is important to group sequences originating from the same gene before the ESTs are assembled to reconstruct the original mRNA. Some clustering algorithms use single-linkage clustering , constructing a transitive closure of sequences with a similarity over a particular threshold.
The PKS genes for a certain polyketide are usually organized in one operon or in gene clusters. Type I and type II PKSs form either large modular protein complexes or dissociable molecular assemblies; type III PKSs exist as smaller homodimeric proteins.