List of the allowed characters for each type of sequences.
A C G T W S M K R Y B D H V N -
A C G U W S M K R Y B D H V N -
A C D E F G H I K L M N P Q R S T V W Y B X Z J U O * -
Nomenclature Committee of the International Union of Biochemistry (NC-IUB) (1986). Proc. Natl. Acad. Sci. USA. 83 (1): 4–8.
Nomenclature and Symbolism for Amino Acids and Peptides. IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983.