A proposed model for interaction of polypeptides with RNA.

Pairs of antiparallel beta polypeptide-chain segments in known protein structures are usually observed to form right-handed double helixes with helix parameters in the same range as those of nucleic acids. We have constructed a model containing only standard bond lengths, bond angles, and dihedral angles in which such a polypeptide double helix fits precisely into the minor groove of an RNA double helix with identical helix parameters. The geometry of the RNA portion is essentially a hybrid between those of the A and A' forms. Hydrogen bonds can be made between the ribose 2'-hydroxyls and polypeptide carbonyl oxygens. Since such precise complementarity between the stable conformations of RNA and polypeptides is unlikely to be merely coincidental, we propose that it played a fundamental role in the initiation of precellular evolution. Specificially, we propose that the two double-helical structures are mutually catalytic for assembly of one another from activated precursors in the prebiotic soup, and moreover that they provide some degree of genetic coding.