= Nucleoprotein complex
A \b[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.<Crystal structure of the nucleosome core particle at 2.8 Å resolution by Karolin Luger and others>[Abstract:146base-pair DNA superhelix, histone octamer and nonuniform binding sites]{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.<Structure of the 30S ribosomal subunit by B. T. Wimberly and others>[Abstract:30S nucleoprotein structure and RNA–protein architecture]{ref}
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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