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	3rd base
U	C	A	G
U	UUU	(Phe/F) Phenylalanine	UCU	(Ser/S) Serine	UAU	(Tyr/Y) Tyrosine	UGU	(Cys/C) Cysteine	U
UUC	UCC	UAC	UGC	C
UUA	(Leu/L) Leucine	UCA	UAA	Stop	UGA	(Trp/W) Tryptophan	A
UUG	UCG	UAG	UGG	G
C	CUU	CCU	(Pro/P) Proline	CAU	(His/H) Histidine	CGU	(Arg/R) Arginine	U
CUC	CCC	CAC	CGC	C
CUA	CCA	CAA	(Gln/Q) Glutamine	CGA	A
CUG	CCG	CAG	CGG	G
A	AUU	(Ile/I) Isoleucine	ACU	(Thr/T) Threonine	AAU	(Asn/N) Asparagine	AGU	(Ser/S) Serine	U
AUC	ACC	AAC	AGC	C
AUA	(Met/M) Methionine	ACA	AAA	(Lys/K) Lysine	AGA	Stop	A
AUG[A]	ACG	AAG	AGG	G
G	GUU	(Val/V) Valine	GCU	(Ala/A) Alanine	GAU	(Asp/D) Aspartic acid	GGU	(Gly/G) Glycine	U
GUC	GCC	GAC	GGC	C
GUA	GCA	GAA	(Glu/E) Glutamic acid	GGA	A
GUG	GCG	GAG	GGG	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