Upstream of the structural gene is a promoter sequence, which can provide a binding site for RNA polymerase and trigger transcription. Near the promoter is a set of DNA called operational genes. Operands will also contain regulatory genes, such as repressor genes, which can encode regulatory proteins, bind them to the operator genes and prevent transcription.
The regulatory gene is not necessarily a part of the operon, but it is located somewhere in the genome. The repressor gene will reach the operator gene and block the transcription of the structural gene. A transcription fragment of prokaryote can be regarded as a transcription unit, also called operon.
Extended data:
Operon is usually composed of more than two coding sequences, promoter sequences, manipulation sequences and other regulatory sequences, which are clustered in series in the genome. The initial sequence is a specific DNA sequence that RNA polymerase binds to and starts transcription.
There are some similar sequences in the specific regions of promoter sequences of many prokaryotic genes, usually in the-10 and -35 regions upstream of the transcription start point, which are called * * * sequences. The * * * sequence of the promoter sequence of Escherichia coli and some bacteria is TATAAT in the-10 region, also known as Pribnow, and TTGACA in the -35 region.
Any base mutation or variation in these * * * sequences will affect the combination of RNA polymerase with the initiation sequence and the initiation of transcription. Therefore, * * * has a sequence that determines the transcriptional activity of the promoter sequence.
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