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.^[1] 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.^[2]

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.^[3][4][5][6]

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.^[7]

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^[8]

See also

• List of genetic codes