  A representation of the genetic code as a six-dimensional Boolean hypercube
is proposed. It is assumed here that this structure is the result of the
hierarchical order of the interaction energies of the bases in codon-anticodon
recognition. The proposed structure demonstrates that in the genetic code there
is a balance between conservatism and innovation. Comparing aligned positions
in homologous protein sequences two different behaviors are found: a) There are
sites in which the different amino acids present may be explained by one or two
"attractor nodes" (coding for the dominating amino acid(s)) and their one-bit
neighbors in the codon hypercube, and b) There are sites in which the amino
acids present correspond to codons located in closed paths in the hypercube.
The structure of the code facilitates evolution: the variation found at the
variable positions of proteins do not corresponds to random jumps at the codon
level, but to well defined regions of the hypercube.
