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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).
Three sequences, UAG, UGA, and UAA, known as stop codons, [note 1] do not code for an amino acid but instead signal the release of the nascent polypeptide from the ribosome. [7] In the standard code, the sequence AUG—read as methionine —can serve as a start codon and, along with sequences such as an initiation factor , initiates translation.
A -1 mitoribosome frameshift occurs at the AGA and AGG codons predicted to terminate the CO1 and ND6 open reading frames (ORFs), and consequently both ORFs terminate in the standard UAG codon. [ 2 ] Incomplete stop codons
The resulting amino acid (or stop codon) probabilities for each codon are displayed in a genetic code logo. [ 57 ] As of January 2022, the most complete survey of genetic codes is done by Shulgina and Eddy, who screened 250,000 prokaryotic genomes using their Codetta tool.
Four novel alternative genetic codes were discovered in bacterial genomes by Shulgina and Eddy using their codon assignment software Codetta, and validated by analysis of tRNA anticodons and identity elements; [3] these codes are not currently adopted at NCBI, but are numbered here 34-37, and specified in the table below.
This is the standard or universal genetic code. This table is found in both DNA Codon Table and Genetic Code (And probably a few other places), so I'm pulling it out so it can be common. By default it's the DNA code (using the letter T for Thymine ); use template parameter "T=U" to make it the RNA code (using U for Uracil ).
Prokaryotes have less strigent start codon requirements; they are described by NCBI table 11. B ^ ^ ^ The historical basis for designating the stop codons as amber, ochre and opal is described in an autobiography by Sydney Brenner [4] and in a historical article by Bob Edgar. [5] As in the standard code, initiation is most efficient at AUG.
That start codon (not necessarily the first) indicates where translation may start. The transcription termination site is located after the ORF, beyond the translation stop codon. If transcription were to cease before the stop codon, an incomplete protein would be made during translation. [3]