While it would in principle be possible to recode every reading frame in the genome entirely, we felt this was extremely risky and could have unpredictable results. The expression of certain genes is controlled by codon usage, and widespread elimination of this form of regulation might lead to swings in gene expression incompatible with viability. Also, some genes contain specific RNA sequences controlling gene expression through frameshifting and other mechanisms, and the extent of such regulation is not known. Hence, with the exception of the introduction of PCRTag re-coding, we consider it is unwise to plan any additional, widespread recoding of ORFs. We are, however, replacing all TAG codons with TAA, allowing for subsequent introduction of new coding schemes with unnatural amino acids, as has been done by the Peter Schultz lab and others developing orthogonal translation systems.