dNaM is an artificial nucleobase containing a 3-methoxy-2-naphthyl group instead of a natural base. When it was originally successfully introduced into DNA for replication in an E. coli semi-synthetic organism, it was paired up with d5SICS. For short it is called X whilst the d5SICS being called Y. d5SICS was replaced by in revised versions due to its improved ability to replicate in a wider range of sequence contexts. X pairs with Y using hydrophobic and packing interactions instead of hydrogen bonding, which occurs in natural base pairs. Inside the semi-synthetic organism, methyl directed mispatch repair pathway (MMR) actually fixes unnatural-natural mispairs, whereas recombinational repair actually cuts out the unnatural. The E. coli semi-synthetic organism managed to hold onto the new