Prometheus 6

The most challenging goal, says Romesberg, will be to incorporate unnatural base pairs into the genetic code of organisms. "We want to import these into a cell, study RNA trafficking, and in the longest term, expand the genetic code and 'evolvability' of an organism."...

"It requires a long effort by multiple laboratories, but I think ultimately it will lead to some important tools," [Eric Kool] says. "The ability to encode amino acids with unnatural base pairs will be quite powerful when it comes." 

Artificial letters added to life's alphabet
13:07 30 January 2008
NewScientist.com news service
Robert Adler

Two artificial DNA "letters" that are accurately and efficiently replicated by a natural enzyme have been created by US researchers. Adding the two artificial building blocks to the four that naturally comprise DNA could allow wildly different kinds of genetic engineering, they say.

Eventually, the researchers say, they may be able to add them into the genetic code of living organisms.