Proteins are assumed to incorporate all of the information necessary for unambiguous folding and specific interaction with every other. but, ab initio structure prediction is frequently not a success due to the fact the amino acid collection itself is in reality now not sufficient to manual among limitless folding opportunities. It appears to be logical to try to locate the "lacking" data in nucleic acids, inside the redundant codon. Statistical analyses of about 35K amino acid co-places in eighty distinct protein structures imply the lifestyles of a weak intra-molecular protein-protein interaction code. Co-finding amino acids are preferentially coded by codons that are complementary in reverse orientation to every other on the 1st and third codon positions, but not always on the 2nd. This code, known as D-1 X 3/RC-three X 1, limits the wide variety of desired amino acid pairs from 20 to ten.three+/-zero.8 (SEM, n=20) and emphasizes the significance of "strictly" described amino acids (those having less synonymous codons). The life of this code does no longer via any manner violate the regarded physicochemical policies of protein folding or interplay. it is advised that the biological source of preferential (particular) amino acid co-locations is the partial complementarity of their codons.