Nucleoproteins

Nucleoproteins are complexes formed by a nucleic acid (DNA or RNA) bound to one or more proteins. The term encompasses chromatin-associated protein complexes, RNA-binding protein assemblies, and viral proteins that package genomes. In cells, nucleoproteins play essential roles in packaging, protection, replication, transcription, and RNA processing.

In eukaryotes, the most familiar nucleoprotein organization is chromatin. DNA wraps around a core of histone proteins to form nucleosomes, the basic units of chromatin. The core octamer consists of two each of histones H2A, H2B, H3, and H4, around which about 146 base pairs of DNA are wound. Histone H1 helps compact chromatin by binding linker DNA. Post-translational modifications of histones regulate access to genetic information, influencing transcription, replication, and repair.

Ribonucleoproteins are another major class of nucleoproteins, where proteins associate with RNA to perform diverse cellular tasks. Examples include ribosomes (ribosomal RNA with ribosomal proteins) for protein synthesis; small nuclear RNPs (snRNPs) and other RNPs involved in RNA splicing; small nucleolar RNPs (snoRNPs) that modify rRNA; and hnRNPs that participate in RNA processing and transport. Telomerase is a notable RNP consisting of an RNA component and protein subunits that extend chromosome ends.

In virology, nucleoproteins often refer to viral proteins that bind and protect the genome, forming the nucleocapsid. These proteins shield viral RNA or DNA from degradation and coordinate replication, transcription, and assembly of new virions. Examples include influenza nucleoprotein and coronavirus nucleocapsid proteins.

Overall, nucleoproteins illustrate how nucleic acids function in concert with proteins to regulate the structure and flow of genetic information.