Francis Crick (right) and James Watson (middle) with Maclyn McCarty (left). Image from Lederberg J, Gotschlich EC (2005) A Path to Discovery: The Career of Maclyn McCarty. PLoS Biol 3(10): e341 doi:10.1371/journal.pbio.0030341 DNA has four “letters” (a,c,t,g) with which to define proteins that are long chains of chemicals called amino…