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In the context of translation, a termination signal is the stop codon on the mRNA that elicits the release of the growing peptide from the ribosome. [2] Termination signals play an important role in regulating gene expression since they mark the end of a gene transcript and determine which DNA sequences are expressed in the cell. [1]
Stop codon (red dot) of the human mitochondrial DNA MT-ATP8 gene, and start codon (blue circle) of the MT-ATP6 gene. For each nucleotide triplet (square brackets), the corresponding amino acid is given (one-letter code), either in the +1 reading frame for MT-ATP8 (in red) or in the +3 frame for MT-ATP6 (in blue).
A GGQ motif in the M domain is critical for peptidyl-tRNA hydrolase (PTH) activity. Unlike in the bacterial version, eRF1–eRF3–GTP binds together into a sub-complex, via a GRFTLRD motif on RF3. Stop codon recognition makes eRF3 hydrolyze the GTP, and the resulting movement puts the GGQ into the PTC to allow for hydrolysis.
When a stop codon is reached, the peptidyl-tRNA bond of the tRNA located in the P-site is cleaved releasing the newly synthesized protein. [1] During the translocation step of the elongation phase, the mRNA is advanced by one codon, coupled to movement of the tRNAs from the ribosomal A to P and P to E sites, catalyzed by elongation factor EF-G. [2]
The human genome encodes a few genes whose mRNA stop codon are surprisingly leaky: In these genes, termination of translation is inefficient due to special RNA bases in the vicinity of the stop codon. Leaky termination in these genes leads to translational readthrough of up to 10% of the stop codons of these genes. Some of these genes encode ...
The termination of translation requires coordination between release factor proteins, the mRNA sequence, and ribosomes. Once a termination codon is read, release factors RF-1, RF-2, and RF-3 contribute to the hydrolysis of the growing polypeptide, which terminates the chain. Bases downstream the stop codon affect the activity of these release ...
A simple gene prediction algorithm for prokaryotes might look for a start codon followed by an open reading frame that is long enough to encode a typical protein, where the codon usage of that region matches the frequency characteristic for the given organism's coding regions. [5]
For each codon (square brackets), the amino acid is given by the vertebrate mitochondrial code, either in the +1 frame for MT-ATP8 (in red) or in the +3 frame for MT-ATP6 (in blue). The MT-ATP8 genes terminates with the TAG stop codon (red dot) in the +1 frame. The MT-ATP6 gene starts with the ATG codon (blue circle for the M amino acid) in the ...