Nonspecific interactions of proteins with nucleic acids. Electrostatic interactions occur between proteins and the DNA backbone. The charged phosphate groups are exposed at the exterior surface of a single-stranded DNA molecule, where positively charged amino acid side chains (Arg, Lys, His) can interact. Hydrogen bonds occur between the protein and the deoxyribose groups in the DNA backbone. Hydrophobic interactions involving the intercalation of Tyr, Trp, or Phe side chains between two stacked bases are also prominent in many cases of nonspecific DNA-protein binding. Similar interactions occur with RNA.