Illustration of the coarse-grained models of polypeptide and nucleotide chains, UNRES and NARES-2P, respectively. In UNRES, the interacting sites are peptide groups (shaded spheres labeled p) and side chains (shaded ellipsoids labeled SC). The white spheres represent α carbon atoms (labeled Cα), which are introduced to define the geometry of the backbone. In NARES-2P, the interacting sites are phosphate groups (blue spheres labeled P) and nucleic-acid bases (blue ellipsoids labeled B). A white sphere represents the sugar ring (labeled S); P and S are used to define the geometry of the backbone. The components of the protein-nucleic acid mean-field interaction in the UNRES+NARES-2P representation are also shown as red dashed lines.