Three prime untranslated region
In Genetics, the 3' UTR (read as 3 prime untranslated region) is a particular section of messenger RNA (mRNA).
Like all strands of nucleic acid, mRNA is directional. One end is the 5' (five prime) end: the other is the 3' (three prime) end. Enzymes read mRNA by starting at a start codon near the 5' end and continuing toward the 3' end.
When an enzyme uses messenger RNA's sequence to build a protein (the process is called translation), it is read in the 5'-3' direction. Amino acids are added to the protein until the enzyme encounters a "stop" codon (three nucleic acids which tell the enzyme to stop). Anything beyond this stop codon is part of the 3 prime untranslated region (3' UTR).
In a diagram:
start stop
codon codon
---------|-------------------|--------- 5'-UTR translated RNA 3'-UTR
Many functional elements occur in the 3' UTR:
- Polyadenylation signals target the mRNA to the ribosome, where it is translated.
- SECIS elements, which can occur in the 3' UTRs of eukaryotic mRNAs, direct the ribosome to translate UGA codons as selenocysteines.
- The Histone downstream element is analogous to polyadenylation in function, but has different sequence characteristics, and is used only for histone genes.