4-letter DNA code gets trickier, may simplify creating stem cells.

DNA is held together by code pairs picked from four bases: A-G-T-C.
(adenine, guanine, thymine and cytosine)
Dr. Zhang's lab has now shown that the fourth code C can be supplied in four additional models when it is written into the DNA.  The extra tags seem to have a role in re-programming stem cells.  "Bring it on".
      Story at Science Daily News.