Nucleic acid quaternary structure
Nucleic acid quaternary structure refers to the interactions between separate nucleic acid molecules, or between nucleic acid molecules and proteins. The concept is analogous to protein quaternary structure, but as the analogy is not perfect, the term is used to refer to a number of different concepts in nucleic acids and is less commonly encountered.
Source: Wikipedia — Nucleic acid quaternary structure (CC BY-SA 4.0)