Nucleoproteins are proteins conjugated with nucleic acids (either DNA or RNA). Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins. Structures Nucleoproteins tend to be positively charged, facilitating interaction with the negatively charged nucleic acid chains. The tertiary structures and biological functions of many nucleoproteins are understood. Important techniques for determining the structures of nucleoproteins include X-ray diffraction, nuclear magnetic resonance and cryo-electron microscopy. Viruses Virus genomes (either DNA or RNA) are extremely tightly packed into the viral capsid. Many viruses are therefore little more than an organised collection of nucleoproteins with their binding sites pointing inwards. Structurally characterised viral nucleoproteins include influenza, rabies, Ebola, Bunyamwera, Schmallenberg, Hazara, Crimean-Congo hemorrhagic fever, and Lassa. Deoxyribonucleoproteins A deoxyribonucleoprotein (DNP) is a complex of DNA and protein. The prototypical examples are nucleosomes, complexes in which genomic DNA is wrapped around clusters of eight histone proteins in eukaryotic cell nuclei to form chromatin. Protamines replace histones during spermatogenesis. Functions The most widespread deoxyribonucleoproteins are nucleosomes, in which the component is nuclear DNA. The proteins combined with DNA are histones and protamines; the resulting nucleoproteins are located in chromosomes. Thus, the entire chromosome, i.e. chromatin in eukaryotes consists of such nucleoproteins. In eukaryotic cells, DNA is associated with about an equal mass of histone proteins in a highly condensed nucleoprotein complex called chromatin. Deoxyribonucleoproteins in this kind of complex interact to generate a multiprotein regulatory complex in which the intervening DNA is looped or wound. The deoxyribonucleoproteins participate in regulating DNA replication and transcription. Deoxyribonucleoproteins are also involved in homologous recombination, a process for repairing DNA that appears to be nearly universal. A central intermediate step in this process is the interaction of multiple copies of a recombinase protein with single-stranded DNA to form a DNP filament. Recombinases employed in this process are produced by archaea (RadA recombinase), by bacteria (RecA recombinase) and by eukaryotes from yeast to humans (Rad51 and Dmc1 recombinases). Ribonucleoproteins A ribonucleoprotein (RNP) is a complex of ribonucleic acid and RNA-binding protein. These complexes play an integral part in a number of important biological functions that include transcription, translation and regulating gene expression and regulating the metabolism of RNA. A few examples of RNPs include the ribosome, the enzyme telomerase, vault ribonucleoproteins, RNase P, hnRNP and small nuclear RNPs (snRNPs), which have been implicated in pre-mRNA splicing (spliceosome) and are among the main components of the nucleolus. Some viruses are simple