Nonhistone chromosomal

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. 

Jackson, J.B., Pollock, J.M., Jr., and Rill, R.L. (1979) Chromatin fractionation procedure that yields nucleosomes containing near-stoichiometric amounts of high mobility group nonhistone chromosomal proteins. Biochemistry 18, 3739-3748. 

Much of the preceding discussion on chromatin structure indicates that active chromatin exists in a more swollen state than inactive chromatin. Several biochemical changes accompany the transition from condensed to swollen chromatin. These changes include a redistribution of nucleosomes along the DNA duplex, chemical modification of histones, alteration in the pattern of nonhistone chromosomal protein binding, and chemical modification of the DNA. Currently, most of these changes are discussed in a general, descriptive manner because their causes and consequences are not known. 

All classes of steroid hormones bind to specific cytoplasmic receptors in their respective target tissues, and are then translocated to the nucleus. For example, testosterone, a lipid-soluble substance, enters the cell and is enzymatically reduced to dihydrotestosterone by 5-a reductase. Dihydrotestosterone then becomes bound to a specific androgen receptor site located in the cytoplasm. This complex becomes activated and is then translocated to the nucleus, where it binds to the chromatin acceptor site consisting of DNA and nonhistone chromosomal proteins. This interaction results in the transcription of a specific messenger RNA that is then relocated to the cytoplasm and translated on the cytoplasmic ribosomes, resulting in the synthesis of a new protein that sponsors the androgenic functions (Figure 61.6). 

How the above described vitamins influence in vitro 3H-tryptophan nuclear receptor binding is not clear. Based upon the experiments with added dithiothreitol, it appears that some vitamins act on the sulfhydryl groups of the receptor, which become modified, which interferes with 3H-tryptophan binding. Reviews of reports by others indicate that certain vitamins can bind to hepatic nuclei. Examples include (1) 3H-a-tocopherol, which has been reported to become incorporated into isolated rat liver nuclei in a nonspecific manner by binding to chromatin nonhistone chromosomal protein,196 and (2) rat liver nuclei, which contain receptors for a folate-binding protein.197 As yet, it is not known whether others act similarly or not. Thus, whether competitive binding to nuclei between vitamins and tryptophan occurs is not known. 

Js HMGl high-mobility group (nonhistone chromosomal) protein 1 13ql2 ... 

Transcription is the first and often most critically regulated step in gene expression. In eukaryotes, multisubunit RNA polymerases transcribe genes, whose DNA is packaged together with histones and other nonhistone chromosomal proteins into chromatin, which is notoriously intractable and not easily transcribed by those polymerases in vitro. A central question driving research on eukaryotic transcription has therefore been, How is timely and efficient transcription of chromatin-embedded genes achieved in eukaryotic cells ... 

James GT, Yeoman LC, Matsui S, Goldberg AH, Busch H (1977) Isolation and characterization of nonhistone chromosomal protein C-14 which stimulates RNA synthesis. Biochemistry 16 2384-2389... 

Components of membrane transformation systems include the nucleus with its DNA, nonhistone chromosomal proteins, and the derived informational molecules (e.g., mRNA) for protein synthesis. The mRNA moves into the cytoplasm through the transformation of membranes. For example, the rough endoplasmic reticulum contains ribosomal RNA with its templates for protein synthesis. The system evolves with cytoplasmic organelles and substrates to influence structure and function. During this process the vacuoles, microtubules, endoplasmic reticulum, subcellular organelles, and plasmalemma may release specific metabolic nitrogenous products (conjugates, enzymes) internally or externally. Some of these may be involves in the biosynthesis of cutin and suberin (76). 

Whether a gene is positioned in active or inactive chromatin certainly also plays a large role in whether or not transcription can occur. The various elements which define active chromatin (sensitivity and hypersensitivity to nucleases, presence of HMG proteins, modifications of both histone and nonhistone chromosomal proteins, DNA methylation) have recently been reviewed (Weisbrod, 1982 Razin and Riggs, 1980). With a few exceptions, there is no clear idea how the DNA sequences and proteins which are known to modulate transcription relate to the formation of active chromatin. Such a discussion must therefore be deferred to a later date. 

Chromatin Cellular genome as nucleoprotein which contains DNA, histones, and a variety of nonhistone chromosomal proteins. 

HMG proteins High mobility group (based on gel electrophoresis) proteins which are associated with chromatin a subset of nonhistone chromosomal (NHC)... 

Walker, J. M., Shooter, K. V., Goodwin, G. H., and Johns, E. W., 1976, The isolation of two peptides from a nonhistone chromosomal protein showing irregular charge distribution within the molecule, Biochem. Biophys. Res. Commun. 70 88. 

Within the nucleus, the hormone-receptor complex binds to the chromatin. The complex binds poorly to purified DNA, however (Chan and O Malley, 1978). The complex appears to be specific for its chromatin, since little binding is observed when non-target-cell chromatin is used. The free hormone also binds poorly to chromatin. Using nonhistone chromosomal proteins from target-tissue chromatin, it is possible to produce hormone-receptor complex binding in non-target-tis-sue chromatin (Spelsberg et al., 1972). 

---