The major accomplishment of the paper referenced in the original article is that they demonstrated the feasibility of unnatural bases in vivo. The work in the Y

The major accomplishment of the paper referenced in the original article is that they demonstrated the feasibility of unnatural bases in vivo. The work in the Yang, et. al. paper occurred in vitro, whereas the Malyshev paper was in an E. coli system. Malyshev, et al. noticed that the unnatural bases were being degraded in the space between inner and outer cell membranes (periplasm), so they added a membrane transport protein to import the unnatural bases into the cell. From there, the E. coli was able to incorporate the unnatural bases into replicates of an introduced DNA segment (plasmid) using its endogenous replication machinery. They also demonstrated that the unnatural bases were not a hinderance to growth, and they they were not excised by the DNA repair enzymes. There have been other papers demonstrating the use of unnatural bases in various cases in vitro (some cited in the paper), but this is notable because it is a thorough example of use in vivo. Peter Schultz has done similar work, as well as exciting work on unnatural bases in tRNA. The bases in the Yang paper and those in the Malyshev paper both exhibit Watson-Crick bonding geometry, and pair by hydrogen bonding. One distinction of those mentioned in the Malyshev paper is the presence of a sulfur substituent, though there is no mention of its participation in the bond.