N Field
The N Field contains a DNA or Protein sequence.
No merge is supported; the imported string replaces the previous one.
The source string can be lowercase, uppercase or a mix of both.
For protein, all letters [a…z] and [A…Z] are supported, except 'J', 'O' and 'U'.
For DNA, combined letters are supported and all letters found in “abcdghkmnrstuvwxy” are accepted. Letters from “efijlopqz” are replaced by ‘X’.