The genetic code as a cipher

Living cells read DNA three letters at a time. Each group of three, called a codon, stands for one amino acid, and each amino acid has a one-letter code like M for methionine. Twenty of the 26 letters are used, so puzzle makers can spell words as DNA.

Paste a string of A, C, G and T, or U for RNA. CacheCrack reads it in threes and shows the letters. Going the other way, it turns your word into codons, using the first codon listed for each amino acid.

Example

ATG GCC is MA.