1. According to the WIPO Standard ST.26 [wipo.int] :In ST.26, uracil and thymine are both represented in the sequence by “t” and without further annotation; “t” represents uracil in RNA and thymine in DNA.
"The symbol “t” will be construed as thymine in DNA and uracil in RNA. Uracil in DNA or thymine in RNA is considered a modified nucleotide and must be further described in the feature table as provided by paragraph 19." - see paragraph 14.
So it is necessary for a user to transform each 'u' symbol to a 't' in an RNA sequence in order that it is compliant with WIPO ST.26. WIPO Sequence will perform this task automatically during an ST.25 import and if the RNA sequence is manually created within a project The symbol “u” must not be used to represent uracil in an RNA molecule in a sequence listing.
For an ST.25 import of an RNA sequence, all "u" will be automatically transformed into "t" by the tool.
WIPO Sequence will not allow you to save an RNA sequence with a "u" in it.continue with the save.