Standard & Non-standard DNA, RNA, and Protein Alphabets

In bioinformatics/computational biology, a sequence is represented by ordered succession of characters (1-letter code of DNA/RNA/amino acid) known as alphabets. The standard type of alphabets include DNA alphabet [A, T, C, G], RNA alphabet [A, U, C, G], and amino acid alphabet [A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, Y]. While, non-standard alphabets include DNA/RNA alphabet [B, D, H, K, M, N, R, S, V, W, Y], and amino acid alphabet [B, J, O, U , X, Z].

List of standard and non-standard DNA/RNA alphabets with 1-letter code is given in table below.

Nucleotide	1-letter code
Adenine	A
C, G, T	B
Cytosine	C
A, G, T	D
Guanine	G
A, C, T	H
G, T	K
A, C	M
A, T, U, C, G	N
A, G	R
G, C	S
Thymine	T
Uracil	U
A, C, G	V
A, T	W
C, T	Y

List of standard and non-standard amino-acid alphabets with 3-letter code and 1-letter code is given in table below.

Amino acid	3-letter code	1-letter code
Alanine	Ala	A
Aspartic acid (or) Asparagine	Asx	B
Cysteine	Cys	C
Aspartic acid	Asp	D
Glutamic acid	Glu	E
Phenylalanine	Phe	F
Glycine	Gly	G
Histidine	His	H
Isoleucine	Ile	I
Leucine (or) Isoleucine	Xle	J
Lysine	Lys	K
Leucine	Leu	L
Methionine	Met	M
Asparagine	Asn	N
Pyrrolysine	Pyl	O
Proline	Pro	P
Glutamine	Gln	Q
Arginine	Arg	R
Serine	Ser	S
Threonine	Thr	T
Selenocysteine	Sec	U
Valine	Val	V
Tryptophan	Trp	W
Any amino acid	Xaa	X
Tyrosine	Tyr	Y
Glutamic acid (or) Glutamine	Glx	Z