'X' in Newbler output

[spiderwing]

I feel silly for asking this, but for some reason I haven't been able to find the answer, which must be buried somewhere in the documentation.

Anyway, I have a number of fasta files generated (not by me) from the Newbler EST assembler. Frequently, the 'X' character will appear in these nucleotide sequences. Do those X's originate from Newbler, and if so are they equivalent to the 'N' wildcard character? I've only seen 'X' as a wildcard in protein sequences, so not really sure what to make of it...