Nuclease sensitivity chromatin

The mechanisms involved in gene aclivatinn and inactivation are major problems in biology, so that transient, or permanent structures associated with such phenomena will continue to attract much attention. There is now evidence for changes in chromatin structure at chromosome sites prior to their becoming transcriptionally active nuclease sensitive sites, enhancers, and promolerx have also been identified at various loci. 

Chromatin remodeling, nucleosome remodeling, and nucleosome disruption are general terms that have been used to summarize a number of changes in chromatin structure. Often, these terms are used to define any event that alters the nuclease sensitivity of a region of chromatin, as nuclease sensitivity is a frequendy used marker of changes in chromatin structure. However, there have been other in vitro assays devised to... 

To assess whether the results obtained with Ho33342 related to some innate feature of cellular chromatin, namely accessibility, permeabilised cells were exposed to a low level of DNase II (under conditions which produced a linear relationship between enzyme concentration and break frequency) and accessibility monitored as the frequency of enzyme-induced DNA strand-breaks. The results (Table 1) show that nuclease sensitivity correlated with the frequency of ligand-induced breaks. 

We emphasize that the distinction between nuclease sensitivity and hype sensitivity is not merely a semantic one. During the activation of gene expression in vivo, it is quite likely that as a first step, a large stretch of chromatin undergoes some stmctural transition to a more accessible conformation (it is possible that such a transi-... 

Wood, W.I. and Felsenfeld, G. (1982) Chromatin structure of the chicken beta-globin gene region. Sensitivity to DNase I, micrococcal nuclease, and DNase II. J. Biol. Chem. 10 257(13), 7730-7736. 

The study of chromatin structure commonly involves the use of nuclease digestion techniques (review [13]) which have previously revealed that transcriptionally active or potentially active regions of chromatin (representing perhaps only 5—10% chromatin) demonstrate enhanced sensitivity or accessibility to endonucleases. Chromatin accessibility has also been studied by the use of various intercalating and cationic probes to nuclear DNA (review [14]). In the present study both a deoxribonuclease and a bis-benzimidazole dye have been used as probes for chromatin organisation. 

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. 

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