Histone oligomers

Hyde and Walker, 1975a) indicate that there are two basic types of histone-histone interactions or contacts those within the nucleosome which result in the formation of histone octamers and those between nucleosomes which give rise to higher oligomers. 

As noted above, salt-extracted H2A H2B will form higher oligomers, fibers could be obtained from salt-extracted histones (Fig. 3c), and even octamers are now known to associate into superstructures at very high salt concentration (Wachtel and Sperling, 1979). It would therefore seem that self-assembly is a general property of histones. The pattern of complex formation of the core histones is shown schematically in Fig. 4. 

Figure 1 Sensing of DSBs by the ATM checkpoint. DSBs trigger the autophosphorylation of ATM and transform the inactive ATM oligomers to active ATM monomers. The MRN complex is important for the recruitment and the activation of ATM at DSBs. ATM phosphorylates the histone H2AX adjacent to the DSBs, which in turn recruits the mediator Mdcl and brings in additional ATM molecules.

Poly(ADP-ribose) synthetase uses NAD as a substrate to catalyze the formation of a homopolymer of repeating ADP-ribose units [1-3]. The oligomers and polymers of ADP-ribose are synthesized in a covalent association with various proteins of which histones and [4-7] and the synthetase itself [8—10] are the best characterized. 

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