code: public static final Character get1LetterCode(String groupCode3) {
  
  		Character code1;
  
  		// is it a standard amino acid ?
  		code1 = get1LetterCodeAmino(groupCode3);
  
  		if (code1 == null) {
  			// hm groupCode3 is not standard
  			// perhaps it is a nucleotide?
  			groupCode3 = groupCode3.trim();
  			if (isNucleotide(groupCode3)) {
  				code1 = nucleotides30.get(groupCode3);
  				if (code1 == null) {
  					code1 = nucleotides23.get(groupCode3);
  				}
  				if (code1 == null) {
  					code1 = UNKNOWN_GROUP_LABEL;
  				}
  			} else {
  				// does not seem to be so let's assume it is
  				// nonstandard aminoacid and label it "X"
  				// logger.warning("unknown group name "+groupCode3 );
  				code1 = UNKNOWN_GROUP_LABEL;
  			}
  		}
  
  		return code1;
  
  	}
docs: Convert a three letter amino acid or nucleotide code into a single
  character code. If the code does not correspond to an amino acid or
  nucleotide, returns {@link #UNKNOWN_GROUP_LABEL}.
  
  Returned null for nucleotides prior to version 4.0.1.
  
  @param groupCode3
  three letter representation
  @return The 1-letter abbreviation