Benutzer:Hoffmeier/UTR

Untranslatierte Regionen (UTR) (engl. untranslated region) sind nicht-codierende Bereiche der mRNA, die nicht translatiert werden.

Schematische Darstellung einer prozessierten eukaryotischen mRNA mit Cap-Struktur, 5'UTR, CDS ORF, 3'UTR und poly(A)-Schwanz.

Man unterscheidet zwischen 5'UTR und 3'UTR der mRNA.

Die 5'UTR reicht vom Transkription-Startpunkt bis vor dem Translation-Startcodon. Die 3'UTR beginnt hinter dem Translation-Stoppcodon bis zum Polyadenylierung-Startpunkt.

A mRNA codes for a protein through translation. The mRNA also contains regions that are not translated: in eukaryotes, the 5' untranslated region, 3' untranslated region, cap and polyA tail.

In prokaryotic mRNA the 5' UTR is normally short. Some viruses and cellular genes have unusual long structured 5' UTRs which may have roles in gene expression.

Several regulatory sequences may be found in the 5' UTR:

• Binding sites for proteins, that may effect the mRNA's stability or translation, for example iron responsive elements, which occur in the 5' UTRs (and 3' UTRs) of a small number of eukaryotic mRNAs that regulate gene expression in response to iron.
• Sequences that promote the initiation of translation.
• Novel Riboswitches

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The three prime untranslated region (3' UTR) is a particular section of messenger RNA (mRNA). It follows the coding region.

An mRNA codes for a protein through translation. The mRNA also contains regions that are not translated. In eukaryotes the cap, 5' untranslated region, 3' untranslated region, and polyA tail (see diagram).

In prokaryotes mRNA structures have some differences (see mRNA) as do histone mRNAs. However, both have 3' UTRs.

Several regulatory sequences are found in the 3' UTR:

• A polyadenylation signal, usually AAUAAA, or a slight variant. This marks the site of cleavage of the transcript approximately 30 base pairs past the signal, followed by the addition of several hundred adenine residues (poly-A tail).
• Binding sites for proteins, that may effect the mRNAs stability or location in the cell, for example the SECIS elements, which occurs in the 3' UTRs of a small number of eukaryotic mRNAs, direct the ribosome to translate some UGA as selenocysteines rather than stop codons, an extension of the genetic code.
• Binding sites for miRNAs a type of RNAi.