what is the function of promoter and terminater in transcription unit?

Function of promoter in transcription:

The term promoter is used to describe all the sequences that are important in the initiation of transcription of a gene.

  • In prokaryotes, the promoter is recognized by RNA polymerase and an associated sigma factor, which in turn are often brought to the promoter DNA by an activator protein's binding to its own DNA binding site nearby.
  • In eukaryotes, the process is more complicated, and at least seven different factors are necessary for the binding of an RNA polymerase-II  to the promoter.

Function of terminator in transcription:

A section of genetic sequence that marks the end of transcription.

In prokaryotes  two classes of transcription terminators are known:

  1. Intrinsic transcription terminators where a hairpin structure forms within the nascent transcript that disrupts the transcription process.
  2. Rho dependent terminators that require Rho- factors an RNA helicase protein complex, to disrupt the nascent mRNA-DNA-RNA polymerase ternary complex.

In eukaryotes,termination of transcription occurs by different processes, depending the type of polymerase utilized.

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1 promoter and 1 terminator is present in a transcription unit.

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