Nucleoprotein complex

The DNA in a eukaryotic cell nucleus during the interphase between cell divisions exists as a nucleoprotein complex called chromatin. The proteins of chromatin fall into two classes histones and nonhistone chromosomal proteins. 

Shetty, J.K., and Kinsella, J.E. (1980) Ready separation of proteins from nucleoprotein complexes by reversible modification of lysine residues. Biochem. J. 191, 269-272. 

Four processes are concerned in the isolation of a nucleic acid. First is the destruction of the tissue structure (stage 1). A nucleoprotein complex is then separated from other cellular constituents (stage 2). This complex is dissociated and the protein is removed (stage 3) and, finally, the nucleic acid is precipitated from the resulting solution (stage 4). Disintegration of... 

In a number of methods, isolation of the nucleoprotein complex (stage 2) is avoided. In the isolation of ribonucleic acid from beef pancreas,1241 nuclear material and cell debris are removed from a normal-saline extract of the minced tissue, which is then brought to half-saturation with sodium chloride (to dissociate the protein from the nucleic acid). After removal of the protein, the nucleic acid is precipitated with alcohol. However, the suggestion has been made126 that it is more satisfactory to isolate the nucleoprotein first, and this has been carried out, for instance, in the extraction of the ribonucleic acid from fowl sarcoma GRCH 15.126 Nucleoprotein complexes have also been isolated from baker s yeast127 and have been separated into various fractions, the nucleic acids from which differ slightly in composition. In addition, nucleoproteins have been isolated by complex formation with cetyltrimethylammonium bromide.128... 

In the past, dissociation of the nucleoprotein complex has been brought about by salt solutions or by heat denaturation,129 but, more recently, decomposition has been effected by hydrolysis with trypsin,126 or by the use of dodecyl sodium sulfate130 or strontium nitrate.131 Some virus nucleoproteins are decomposed by ethyl alcohol.132 This effect may be similar to that of alcohol on the ribonucleoproteins of mammalian tissues. If minced liver is denatured with alcohol, and the dried tissue powder is extracted with 10% sodium chloride, the ribonucleoproteins are decomposed to give a soluble sodium ribonucleate while the deoxyribonucleoproteins are unaffected.133 On the other hand, extraction with 10 % sodium chloride is not satisfactory unless the proteins have first been denatured with alcohol. Denaturation also serves to inactivate enzymes of the tissues which might otherwise bring about degradation of the nucleic acid during extraction. 

DNA is packaged in the nucleus into the form of chromatin. Chromatin is a nucleoprotein complex composed of histone and non-histone proteins, DNA and RNA and it exhibits a repeating structure (van Holde, 1988). The basal unit of chromatin, the nucleosome, is composed of a histone octamer (two each of H2A, H2B, H3 and H4) around which two superhelical turns of DNA are wrapped (van Holde, 1988). The structure of both the histone octamer (Arents et al, 1991)... 

Pauli, T.T. and Johnson, R.C. (1995) DNA looping by Saccharomyces cerevisiae high mobility group proteins NHP6A/B. Consequences for nucleoprotein complex assembly and chromatin condensation. J. Biol. Chem. 270, 8744-8754. 

In this chapter we have presented a brief struetural overview of the modifications of the primary structure and at the post-translational level that contribute to histone variability. We have also diseussed the different contributions of histones and DNA to the stability and dynamies of the ehromatin nucleoprotein complex. In Section 6 we have integrated both topies using several representative examples from experimental results available from reeent and past literature. The results described in this section provide a good example of the dual informational and structural role of histone variability. 

The HMf-nucleoprotein complexes can be considered bona fide chromatin structures ... 

In the nuclei of eukaryotes (see p. 196), DNA is closely associated with proteins and RNA. These nucleoprotein complexes, with a DNA proportion of approximately one-third, are known as chromatin. It is only during cell division (see p. 394) that chromatin condenses into chromosomes that are visible under light microscopy. During interphase, most of the chromatin is loose, and in these conditions a morphological distinction can be made between tightly packed heterochromatin and the less dense euchromatin. Euchro-matin is the site of active transcription. 

Viruses are parasitic nucleoprotein complexes. They often consist of only a single nucleic acid molecule (DNA or RNA, never both) and a protein coat. Viruses have no metabolism of their own, and can therefore only replicate themselves with the help of host cells. They are therefore not regarded as independent organisms. Viruses that damage the host cell when they replicate are pathogens. Diseases caused by viruses include AIDS, rabies, poliomyelitis, measles, German measles, smallpox, influenza, and the common cold. 

An active bending of the DNA induced by regulatory proteins is of particular importance when a defined arrangement of the DNA in a small volume within a larger nucleoprotein complex is required. 

Newly synthesized mRNA emerges from the nuclear pores as nucleoprotein complexes containing as many as ten different proteins. A major component is a 78-kDa polypeptide thought to be associated with the poly(A) tail. These ribonucleoproteins are sometimes stored for long periods of time, for example, in mature seed embryos and in amphibian oocytes.5753/674 They may also travel rapidly for long distances, e.g., down nerve axons675 or from cell to cell in plants via transport in the phloem.676... 

Huang W, Shostak Y, Tarr P, Sawyers C, Carey M. Cooperative assembly of androgen receptor into a nucleoprotein complex that regulates the prostate-specific antigen enhancer. J Biol Chem 1999 274 25756-25768. 

MICROSOME A phospholipid-nucleoprotein complex derived from the ribosomes and endoplasmic reticulum of eukaryotic cells site of diverse enzymatic reactions important in the metabolism of toxicants and other chemicals. 

Protein and Nucleic Acid Interactions The Nucleoprotein Complex... 

Separation of "Proteins from the Nucleoprotein Complex in Yeast by Succinylation Procedure... 

Based on these experimental data an integrated procedure for separating protein and NA is proposed. This procedure, which is outlined in Scheme III, is an extremely practical procedure for isolating and separating proteins from yeast nucleoprotein complexes. For their successful use in foods, the digestibility, the nutritional, and functional... 

Scheme III. Scheme for separating proteins and nucleic acids from a nucleoprotein complex using reversible modifying reagents of amino groups in the proteins...

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