What symbols should be used for representing nucleotides in a sequence listing?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

The MPEP 2423.01 specifies the symbols to be used for representing nucleotides in a sequence listing:

“The bases in nucleotide sequences must be represented using the one-letter code for nucleotide sequence characters. Only lower case letters in conformity with the list given in WIPO Standard ST.25 (1998), Appendix 2, Table 1, may be used.”

The approved one-letter codes for nucleotides are:

• a – for adenine
• c – for cytosine
• g – for guanine
• t – for thymine in DNA or uracil in RNA

It’s important to note that only lowercase letters should be used, as specified by the WIPO Standard ST.25.