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What are Nucleoproteins?

Nucleoproteins are a type of proteins that are associated with the nucleic acids and ribosomes and lipoproteins, they often serve as a transport of lipids and storage proteins like vitelline. Nucleoprotein is a conjugated protein structure consisting of a protein that is linked to a nucleic acid, either DNA abbreviated as deoxyribonucleic acid or RNA abbreviated as ribonucleic acid. The protein that is combined with DNA is commonly either histone or protamine, thus the resulting nucleoproteins are found in chromosomes. Many viruses are little more than organized collections of deoxyribonucleoprotein. Less information is known about the proteins that are linked with RNA unlike protamine and histone, which appear to contain the amino acid tryptophan.

Norman Pirie who was a British biochemist and virologist along with the help of Frederick Bawden discovered that the virus could be crystallized by insulating the tomato bushy stunt virus into it, it was discovered in the year 1936. This is considered a significant milestone in the understanding of DNA and RNA. The viruses are nucleoproteins among these viruses the structurally characterized ones are Ebola,  rabies,  Schmallenberg, influenza, Bunyamwera, Hazara, Lassa, and Crimean-Congo hemorrhagic fever. Casein the milk protein is nucleoprotein is one of the examples of nucleoproteins.

Biochemistry of Nucleoproteins

In research, nucleoproteins from a wide variety of animal cells have been prepared to find their biochemistry. It has been prepared from the major organs of the mammals, these include liver, kidney, pancreas, spleen, thymus, brain, spleen, and some of the blood cells of the dogfish, and from the sperm of the shad, frogs, and sea urchin. These nucleoproteins are found located in the nuclei of the cells from which the mentioned ones are derived.

The most striking characteristics of these nucleoproteins are their viscosity and bi-refractiveness of the substance that can flow when present in the solution and their fibrous nature when precipitated. These properties indicate that the nucleoprotein molecule is markedly elongated. The phosphorus content found in the nucleoprotein of Arbacia sperm is about 3.05 percent, of trout sperm 6.55 percent, and of the nucleoproteins that are prepared from the mammalian organs can have in between 3.7 and 4.4 percent. In all of these organs, the phosphorus content is in the form of desoxyribose nucleic acid. 

The nucleic acid content of the nucleoproteins can range from 31 to 66 percent. From each of these nucleoproteins, the nucleic acid has been isolated and it is shown to have a composition that is expected to approximating the tetranucleotide theory. These nucleic acids resemble the highly polymerized nucleic acid that is prepared from the thymus gland. It exhibits the property of high viscosity and birefringence or birefractiveness of flow when present in the solution and in forming long fibers when they are precipitated. The protein component of the nucleoprotein complex has in each instance been prepared. These proteins are histones and protamines. They have a high nitrogen content and some of the basic properties. 

The ultra-violet absorption spectra of the nucleoproteins show that the intense absorption at 2540 A⁰ due to the high concentration of nucleic acid content that is present. The protein part of the complex is maximum at 2750 A⁰, slightly these are removed from the maximum at 2800 A⁰ of a certain typical protein such as egg albumin.

The nucleoproteins that are prepared from the mammalian organs can spread at an air-water interface at a pH range of four. In case if a little amount of heptyl alcohol is added to the solution. Then the thick film is formed when it is measured by the method of Langmuir and Blodgett is 15 - 16 A⁰. The protein component can alone spread readily, without the help of heptyl alcohol, at a pH level of 8.3 to provide a film, to represent the characteristic of other proteins. The spreading experiments that are conducted on the nucleoprotein and on its separated components can show that under certain conditions the protein and nucleic acid can combine to form a complex. 

Importance of Nucleoproteins

We have seen the biochemistry of nucleoproteins now lets us study why the structure is important, what its classification looks like. 

The structure of nucleoproteins is of importance because, in the cell nucleus, DNA is almost completely complexed with the proteins, and the transference of the genetic information from the DNA to RNA takes place. Hence to the synthetic mechanisms, it is likely to be profoundly modified that by the presence of the protein. The existence of this complex is in a stable form that appears to be essential to the structure of the chromosome since the agents to which they dissociate the complex and also disrupt the structure of the chromosome. After the early interest in the protein component, the attention was largely directed to the DNA. In recent years, the nuclear proteins and the nature of their complex with the DNA structure have again been the subject of study. The nature of the interaction of the RNA-protein complex of ribosomes is largely unknown.

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Nucleoproteins found in the body are frankly acidic in nature and these are soluble in alkalies with which they form a salt. They are precipitated from their solutions by the acetic acid and then they are redissolved by dilute HCL. They are not coagulated but they can exhibit the precipitation and color reactions as a characteristic of the protein substances that are present. Their importance lies in the increasing evidence that they are closely associated with the chromosomes of the cells. In some of the bacteria cells, these substances have been demonstrated, which can transform one genetic type of bacteria into another genetic strain. These genetic strains have been proven to be deoxyribonucleic acid.


A deoxyribonucleoprotein or DNP is a complex of DNA molecule and protein. The prototypical examples are some of the nucleosomes, these are the complexes in which the genomic DNA is wrapped around some of the clusters of eight histone proteins present in eukaryotic cell nuclei to form chromatin. Protamines can replace the histones during spermatogenesis.

Functions of DNP Include:

The most widely spread deoxyribonucleoproteins are nucleosomes, in which the component is nuclear DNA. The proteins that are combined with DNA are histones and protamines thus the resulting nucleoproteins are found located in chromosomes. Thus, the entire chromosome, including the chromatin in the eukaryotes consists of such nucleoproteins.

In eukaryotic cells, the 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 can interact to generate a multiprotein regulatory complex, among which the intervening DNA is looped or wound. The deoxyribonucleoproteins participate in the regulation of the DNA molecule replication and transcription.

Deoxyribonucleoproteins are also involved in homologous recombination, it is a process for repairing the DNA that appears to be nearly universal. A central intermediate step in this process is that the interaction of the multiple copies of a recombinase protein with the single-stranded DNA in order to form a DNP filament. Recombinases that are employed in this process are produced by archaea by bacteria and by eukaryotes from yeast to humans.


A ribonucleoprotein or RNP is a complex structure that is a combination of ribonucleic acid and RNA-binding protein. These are the complexes that play an integral part in a number of important biological functions. These functions include transcription, translation, regulating gene expression, and regulating the metabolism of RNA. A few examples of RNPs include the ribosome,  vault ribonucleoproteins, RNase P, the enzyme telomerase, hnRNP, and small nuclear RNPs. These have been implicated in pre-mRNA splicing and are among the main components of the nucleolus. Some of the viruses are simple ribonucleoproteins, that are containing only one molecule of RNA and a number of identical protein molecules. 

Others are the ribonucleoprotein or deoxyribonucleoprotein complexes that are containing a number of different proteins and exceptionally more nucleic acid molecules. Some of the common features of protein-RNA interfaces were deduced based on known structures. For example, RNP in snRNPs has an RNA-binding motif in its RNA-binding protein. Aromatic amino acid residues present in this motif result in stacking interactions with RNA. Lysine residues present in the helical portion of the RNA-binding proteins can help to stabilize the interactions with the nucleic acids. This nucleic acid binding is strengthened by the electrostatic attraction between the positive lysine side chains and the negative nucleic acid phosphate backbones. Although these computational methods of deducing the RNP structures are less accurate than that of the experimental methods. These can provide a rough model of the structure which allows for predictions of the identity of significant amino acids and nucleotide residues. Such information helps in understanding the overall function of the RNP.

'RNP' can also refer to ribonucleoprotein particles. Ribonucleoprotein particles that are are distinct intracellular foci for post-transcriptional regulation. These are the particles that play an important role in influenza A virus replication. The influenza viral genome is made up of eight ribonucleoprotein particles that are formed by a complex of negative-sense RNA which is bound to a viral nucleoprotein. Each of these RNP that carries with it is an RNA polymerase complex. When the nucleoprotein binds to the viral RNA, it is able to expose certain nucleotide bases which allow the viral polymerase to transcribe to the RNA. At this point, once the virus enters a host cell it will be prepared to begin the process of replication.

Anti-RNP antibodies are the autoantibodies that are associated with the mixed connective tissue disease and these are also detected in nearly 40% of Lupus erythematosus patients. There are two types of anti-RNP antibodies that are closely related to Sjogren's syndrome these are SS-A (Ro) and SS-B (La). Autoantibodies against the snRNP are called Anti-Smith antibodies. The presence of a certain significant level of anti-U1-RNP can also serve as a possible indicator when it is detected in conjunction with several other factors.

Functions of RNP Include:

The ribonucleoproteins play an important role in protection. The mRNAs can never occur as free RNA molecules in the cell. They are always associated with certain ribonucleoproteins and can function as ribonucleoprotein complexes.

In the same way, the genomes of the negative-strand RNA viruses can never exist as free RNA molecules. The ribonucleoproteins can protect their genomes from RNase. Nucleoproteins are often acted as the major antigens for viruses because they have certain strain-specific and group-specific antigenic determinants.


Nucleoproteins are certain proteins that are associated with nucleic acids. They can serve in many of the functional roles such as enzymes. For example, an enzyme telomerase used in modifying the nucleic acid, or structural ones, with the histones present in packaging chromatin. The nucleoproteins that are found in vertebrate viruses are synthesized in the cytoplasm. The nucleoprotein does not exist in the helical form at the site of synthesis but rather it is observed as a single strand. Nucleoproteins consist of protein parts and nucleic acids. Where the protein part is made up of protamine and histone and the nucleic acids are the DNA and RNA.

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FAQs on Nucleoproteins

1. The Viruses are Nucleoproteins. Why are They Called So?

Ans: Nucleoprotein is a complex in which protein is associated with the nucleic acid. Viruses have nucleic acid and proteins which assemble themselves into a structure called nucleoproteins or nucleocapsid. This is the reason why viruses are called nucleoproteins.

2. Where are the Nucleoproteins Found in the Body? Which is the Milk Protein That Acts as a Nucleoprotein?

Ans: Nucleoproteins are found in the body in the cell, especially in the context of nucleic acids that are present in the chromosomes. The milk protein that acts as a nucleoprotein is casein.

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