A nucleoprotein complex is an assembly containing both nucleic acid and protein components. The nucleic acid can be DNA or RNA, and its spatial arrangement and contacts with the proteins are part of the structure. A mixture that merely contains both kinds of molecule is not automatically one associated complex.
The nucleosome core particle is a concrete DNA–protein example. The1997 structure reported by Karolin Luger and colleagues contains146 base pairs of DNA wrapped around a histone octamer. It shows both protein–protein and protein–DNA contacts. Counting the components and mapping their contacts answer different questions: eight histone molecules do not imply eight identical DNA-binding environments.[ref]
A bacterial small ribosomal subunit provides an RNA–protein example. Its 16S ribosomal RNA and ribosomal proteins form an organized assembly used in translation. The2000 crystal structure links the RNA/protein arrangement to earlier biochemical observations, showing why the nucleic acid is a structural participant rather than merely something carried inside a protein shell.[ref]
Structure of the 30S ribosomal subunit by B. T. Wimberly and others. Abstract:30S nucleoprotein structure and RNA–protein architecture
An experiment must also distinguish association from coincidental presence. Co-purification can suggest a complex, while a resolved structure can identify actual contacts; neither an ingredient list nor a bulk protein measurement alone specifies the architecture.
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