“The UAG codon is like a fork in the road, where it can be interpreted either as a stop codon or as a pyrrolysine residue,” Shalvarjian said in a press statement. […] Preliminary findings suggest that the archaea’s choice isn’t completely random. When the amino acid is flooding the cell, the microbe tends to interpret UAG as integrated pyrrolysine and turn it into the appropriate protein. However, when less of it was around, UAG often acted as a stop codon, which yields a different protein entirely.