Nucleo-protein structures and protein foldings. The distance between bases in nucleic acids (horizontal blue lines) and amino acids in proteins (red dots) is almost the same (A). This suggests the possibility of residue-level interactions between these molecules (B). Partial, sub-optimal complementarity between DNA strands ("honeycomb structure") and fitting of amino acids into DNA cavities was suggested by Gamow [16, 17] (C, D). A further development of this model is that partial complementarity between mRNA subsequences (E, F) determines the orientation of amino acid residues in ribonucleoprotein complexes and consequently the RNA loops serve as templates (RNA chaperons) to main secondary protein structures such as alpha helices (G) and beta-sheets (H). Codon boundaries are not indicated in these models. The Figure illustrates the historical development of the concept of direct and specific nucleic acid – protein interactions and its possible consequences for protein folding.