# Vertebrate mitochondrial code

The vertebrate mitochondrial code (translation table 2) is the genetic code found in the mitochondria of all vertebrata.

## Evolution

AGA and AGG were thought to have become mitochondrial stop codons early in vertebrate evolution. However, at least in humans it has now been shown that AGA and AGG sequences are not recognized as termination codons. 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.

## Incomplete stop codons

Mitochondrial genes in some vertebrates (including humans) have incomplete stop codons ending in U or UA, which become complete termination codons (UAA) upon subsequent polyadenylation.

## Translation table

| Amino acids biochemical properties | nonpolar | polar | basic | acidic | Termination: stop codon |
Mitochondrial genetic code :
| 1st base | 2nd base | 2nd base | 2nd base | 2nd base | 2nd base | 2nd base | 2nd base | 2nd base | 3rd base |
| 1st base | U | U | C | C | A | A | G | G | | 3rd base |
| U | UUU | (Phe/F) Phenylalanine | UCU | (Ser/S) Serine | UAU | (Tyr/Y) Tyrosine | UGU | (Cys/C) Cysteine | U |
| U | UUC | (Phe/F) Phenylalanine | UCC | (Ser/S) Serine | UAC | (Tyr/Y) Tyrosine | UGC | (Cys/C) Cysteine | C |
| U | UUA | (Leu/L) Leucine | UCA | (Ser/S) Serine | UAA | Stop | UGA | (Trp/W) Tryptophan | A |
| U | UUG | (Leu/L) Leucine | UCG | (Ser/S) Serine | UAG | Stop | UGG | (Trp/W) Tryptophan | G |
| C | CUU | (Leu/L) Leucine | CCU | (Pro/P) Proline | CAU | (His/H) Histidine | CGU | (Arg/R) Arginine | U |
| C | CUC | (Leu/L) Leucine | CCC | (Pro/P) Proline | CAC | (His/H) Histidine | CGC | (Arg/R) Arginine | C |
| C | CUA | (Leu/L) Leucine | CCA | (Pro/P) Proline | CAA | (Gln/Q) Glutamine | CGA | (Arg/R) Arginine | A |
| C | CUG | (Leu/L) Leucine | CCG | (Pro/P) Proline | CAG | (Gln/Q) Glutamine | CGG | (Arg/R) Arginine | G |
| A | AUU | (Ile/I) Isoleucine | ACU | (Thr/T) Threonine | AAU | (Asn/N) Asparagine | AGU | (Ser/S) Serine | U |
| A | AUC | (Ile/I) Isoleucine | ACC | (Thr/T) Threonine | AAC | (Asn/N) Asparagine | AGC | (Ser/S) Serine | C |
| A | AUA | (Met/M) Methionine | ACA | (Thr/T) Threonine | AAA | (Lys/K) Lysine | AGA | Stop | A |
| A | AUG | (Met/M) Methionine | ACG | (Thr/T) Threonine | AAG | (Lys/K) Lysine | AGG | Stop | G |
| G | GUU | (Val/V) Valine | GCU | (Ala/A) Alanine | GAU | (Asp/D) Aspartic acid | GGU | (Gly/G) Glycine | U |
| G | GUC | (Val/V) Valine | GCC | (Ala/A) Alanine | GAC | (Asp/D) Aspartic acid | GGC | (Gly/G) Glycine | C |
| G | GUA | (Val/V) Valine | GCA | (Ala/A) Alanine | GAA | (Glu/E) Glutamic acid | GGA | (Gly/G) Glycine | A |
| G | GUG | (Val/V) Valine | GCG | (Ala/A) Alanine | GAG | (Glu/E) Glutamic acid | GGG | (Gly/G) Glycine | G |
    $^A$ The codon AUG both codes for methionine and serves as an initiation site: the first AUG in an mRNA's coding region is where translation into protein begins.

## Differences from the standard code

| DNA codons | RNA codons | This code (2) | Standard code (1) |
| AGA | AGA | STOP = Ter (*) | Arg (R) |
| AGG | AGG | STOP = Ter (*) | Arg (R) |
| ATA | AUA | Met (M) | Ile (I) |
| TGA | UGA | Trp (W) | STOP = Ter (*) |

### Alternative initiation codons

* Bos: AUA
* Homo: AUA, AUU
* Mus: AUA, AUU, AUC
* Coturnix, Gallus: also GUG