nucleoprotein

Nucleoprotein is a complex of nucleic acid with proteins, forming core components of many cellular and viral particles. In cells, nucleoproteins include histones and non-histone proteins that bind DNA or RNA to organize chromatin, regulate transcription, RNA processing, and transport. Histones are highly basic proteins around which DNA winds to form nucleosomes, the basic unit of chromatin.

In virology, nucleoprotein is typically a structural protein that binds viral RNA or DNA to protect the genome, package it into virions or replication complexes, and coordinate genome replication with polymerases. Viral nucleoproteins often contain RNA-binding motifs and interact with the viral polymerase complex to form ribonucleoprotein particles. For example, the influenza A virus nucleoprotein binds viral RNA and forms RNPs with the polymerase, enabling transcription and replication inside the host cell. Many negative-sense RNA viruses encode a nucleoprotein that is essential for genome stability and replication, while positive-sense viruses use other strategies but also assemble nucleoprotein complexes during replication.

In a broader sense, nucleoproteins include heterogeneous nuclear ribonucleoproteins (hnRNPs) and other RNA-binding proteins that associate with RNA to regulate splicing, export, localization, and translation. These complexes are dynamic and can participate in phase-separated compartments such as stress granules or processing bodies. The term emphasizes protein-nucleic acid interactions that influence nucleic acid metabolism and genome maintenance.