Terminator (genetics)

Transcription terminator as a terminator or a portion of a genetic sequence on the DNA is referred to, which indicates the end of a gene or operon. It leads to the termination of transcription.

In prokaryotes, two classes of transcriptional terminators are known:

  • Intrinsic transcription terminators
  • Rho- dependent transcription terminators

The terminator is usually of a short sequence ( 4-10) of GC base pairs, and are located within the RNA almost immediately after the stop codon, which describe the end of the ORF. Proteins block the termination of transcription is called anti- terminators.

Rho- independent termination

In this form of termination results in the formation of a hairpin-like secondary structure in the RNA transcript. The reason lies in the specific base sequence. The optimal structure for an intrinsic terminator is as follows:

  • Stem -forming GC -rich region 1 (6-8 base pairs)
  • Loop -forming region (3-5 base pairs)
  • Stem -forming GC -rich region 2 (6-8 base pairs)
  • Poly uracil region (3-8 base pairs)

The two GC -rich regions of overlap along the so-called strain. The region here intermediate forms the so-called loop or loop. From this hairpin structure results in a long pause in elongation. This correlates directly proportional to the stability of the hairpin structure. The following thereupon 3-8 uracil residues destabilize the elongating. The current theory is that the hairpin structure of the RNA / DNA hybrid is shortened and the unstable AU pairing further destabilize the complex. The consequence of this is the release of the transcript.

Importance of the hairpin structure for the termination

The hairpin structure contributes in two ways to the Termination for

  • The RNA hairpin structure leads to an allosteric inhibition of nucleotide addition at the active site. Thus, the RNAP is stopped.
  • The hairpin structure provides a separation of the RNA -DNA hybrid in the 5'-end.

Rho -dependent termination

In the rho - dependent termination can be found, as opposed to intrinsic terminators, no destabilizing DNA sequence elements. Here the termination is catalyzed by the termination factor Rho. Is here used to destabilize the elongation complex by the helicase activity of Rho factor. Rho hexamer seen here as C-rich segments on the transcript. It binds to an approximately 100 bp upstream of the elongating region lying on the newly synthesized RNA transcript. Rho moves its ATPase activity due to the 3'- end of the RNA. By this helicase the termination factor, there is a separation of the RNA / DNA hybrid. The result is dissociation of the elongation complex, and the resulting release of the RNA transcript.

Distinction

The terminator sequences at the DNA to be distinguished from the Terminatorcodons on the mRNA, leading to the termination of translation.

Open reading frame Science (journal)
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