Evo. 34: 331, 1992) constant across nature, and entirely constant for the nuclei of the higher creatures. (* This is one more piece of evidence that evolution has occurred on the grand scale, since the code is apparently arbitrary.) Restriction enzymes (endonucleases): Enzymes, mostly from bacteria, that cleave (digest) DNA at specific sequences. * EcoR1, still the champ, cleaves at GAATTC. De