Nucleosome biological functions

Similar results were obtained from reconstitution experiments with DNA and a non-cross-linked octamer (Thomas and Butler, 1978). Nucleosome-like particles were observed in the EM and a pattern of histone cross-linking comparable to that of native chromatin was obtained. However, only 140-base-pair repeats were obtained upon micrococcal nuclease digestion instead of 200-base-pair repeats obtained for native rat liver chromatin (Noll and Komberg, 1977). This indicates that, in the absence of HI, only core particles can be reconstituted. Nevertheless, these studies with both cross-linked and reassembled un-cross-linked histones demonstrate that the octamer is a complete biological functional unit retaining the information for folding the DNA around the histone core. 

DNA Is Involved In several biological functions requiring substantial changes In conformation. For example, the Intrinsically stiff DNA molecule Is wrapped fairly tightly about histones In nucleosomes, and this entire complex must be partially unraveled during replication and transcription. The ability of DNA to assume several different conformational forms In response to Its solid and solution environments has been evident for some time. Recent applications of spectroscopic methods sensitive to molecular dynamics have Indicated that double stranded DNA can also undergo rapid local motions of significant amplitude. 

PARP-1 is an abundant ( 1 to 2 million molecules per cell) and ubiquitous nuclear protein that plays important roles in a variety of cellular functions. One aspect of PARP-1 biology is the modulation of chromatin structure through direct nucleosome binding, covalent modification of chromatin proteins, or the production of PAR which can serve as a polyanionic matrix for the binding of chromatin proteins. Given its role in a variety of physiological and pathophysiological processes, PARP-1 has... 

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