Polynucleosome

In isolated nuclei from rat liver and kidney, Ni2 + was bound to chromatin, polynucleosomes and to deproteinized DNA [339]. Ni2+ directly interacted with stable binding sites on the DNA molecule in chromatin and was associated with histone and nonhistone nuclear proteins [339, 340]. 

Bazett-Jones, D.P., Cote, J., Landel, C.C., Peterson, C.L., and Workman, J.L. (1999a) The SWI/ SNF complex creates loop domains in DNA and polynucleosome arrays and can disrupt DNA-histone contacts within these domains. Mol. Cell. Biol. 19(2), 1470-1478. 

Schnitzler, G.R., Cheung, C.L., Hafner, J.H., Saurin, A.J., Kingston, R.E., and Lieber, C.M. (2001) Direct imaging of human SWI/SNF-remodeled mono- and polynucleosomes by atomic force microscopy employing carbon nanotube tips. Mol. Cell. Biol. 21, 8504-8511. 

Higher levels of organization Nucleosomes can be packed more tightly to form a polynucleosome (also called a nudeofilament). This structure assumes the shape of a coil, often referred to as a 30-nm fiber. The fiber is organized into loops that are anchored by... 

Poirer, G.G., de Murcia, G., Jongstra-Bilen, J., Niedergang, C. and Mandel, P. (1982) Poly(ADP-ribosyl)ation of polynucleosomes causes relaxation of chromatin structure. Proc. Natl. Acad. Sci. USA, 79, 3423-3427. 

Figure 3-8. A polynucleosome. (Adapted from Olins DE and Olins AL Nucleosomes The structural quantum in chromosomes. American Scientist 66 (1978), p 708.)...

Schmitz KS, Lu M, Gauntt J. Influence of ionic strength on the diffusion of polystyrene latex spheres, bovine serum albumin, and polynucleosomes. J Chem Phys 1983 78 5059-5066. 

Repeating units of nucleosome plus linker DNA constitute the polynucleosome, which in turn is involved in higher orders of chromatin structure 50, 63,116,117,123,194). It has been postulated, based on electron micrographs, that polynucleosomes coil into a solenoid with 100 A hole through the central axis 50, 63, 116, 117, 123, 194) one turn of a helix includes 7 to 9 nucleosomes 171). 

When rat pancreatic polynucleosomes were poly(ADP-ribosylated) with purified calf thymus poly(ADPR) polymerase and examined by electron microscopy a relaxation of their native zigzag structure was observed, even at high ionic strengths they showed a close resemblance to chromatin depleted of histones HI. The relaxed state of poly(ADP-ribosylated) polynucleosomes was also confirmed by sedimentation velocity analysis [19, 20]. Locally relaxed regions can also be generated within poly-nucleosome chains by the activity of their intrinsic poly(ADPR) polymerase and appeared to be correlated with the formation of hyper(ADP-ribosylated) forms of histone HI and an increase of DNA polymerase activity [21]. The posttranslational transitory modifications of histones are potential modulators of chromatin stmcture. This may be involved in DNA transcription, replication, and repair. 

Poirier GG, De Murda G, Jongstra-Bilen J, Niedergang C, Mandel P (1982) Poly(ADP-ribosyla-tion) of polynucleosomes causes relaxation of chromatin structure. Proc Natl Acad Sd USA 79 3423-3427... 

At high NAD concentrations, i.e. > 10 /xAf, we have shown previously that the main histone acceptor in polynucleosomes is histone HI [8, 9]. However recently, we have found that core histones could be poly(ADP-ribosyl)ated by the intrinsic activity of the enzyme at low NAD concentrations, i.e. < 1 ijM [10]. We have also suggested that, depending on the automodification state of the enzyme, the core histones and other core nucleosome proteins may become more accessible to poly(ADP-ribose) polymerase [10]. 

Effect of Poly(ADP-Ribosyl)ation on Native Polynucleosomes... 

Concomitantly, structures resulting from the poly(ADP-ribosyl)ation of native chromatin, chromatin-Hl and core particles were examined by electron microscopy. We found, as described earlier for pancreatic chromatin [6, 7], that calf thymus chromatin adopts a more relaxed conformation upon poly(ADP-ribosyl)ation by purified calf thymus poly(ADP-ribose) polymerase free of its DNA (Fig. 3a,d). It was also found that this chromatin exhibited a lower sedimentation velocity as compared to control chromatin [6]. And recently, it has been shown that DNA polymerase a activity is more than twofold higher in the presence of pancreatic polynucleosomes ADP-ribosylated as compared to control polynucleosomes [16]. In striking contrast, no ultrastructural effect was observed when chromatin depleted of histone HI was poly(ADP-ribosyl)ated (Fig. 3b, e). 

Fig. 6. Interaction between poly(ADP-ribose) and chicken erythrocyte core particles. [ P]-poly-(ADP-ribose) was synthesized by purified poly(ADP-ribose) polymerase incubated with calf thymus polynucleosomes and the polymer was extracted as described by Miwa et al. [26]. Core carticles and the polymer were allowed to interact and then centrifuged on a 5-20% (w/v) isokinetic sucrose gradient containing 40 vM NaCl, 10 xM Iris, 0.2 mM EDTA at pH 7.4. Centrifugation was for 14 h at 40,000 rpm (4°C) in a SW41Ti Beckman rotor...

Indeed, these results conelate well with other results we have obtained when polynucleosomes were poly(ADP-ribosyl)ated with their intrinsic activity [10]. In these experiments, we found that when the enzyme has a low level of modification, it modifies histones H2B, H2A and protein A24. However, when it was allowed to modify chromatin at high substrate concentrations, it appeared to have access to histone HI only. Thus, it is tempting to suggest that a histone HI containing chromatin domain, which has also some histone H2B modification, will not recondense. 

Furthermore, some of our preliminary studies indicate that the turnover of poly-(ADP-ribosyl)ated proteins on polynucleosomes leads in time to an extensive modification of histone H2B. Thus, it is conceivable that during DNA repair in vivo, histone H2B modification results in destabilization of condensed chromatin and thereby permits increased accessibility to repair enzymes. Similarly, in active chromatin, where HI levels are greatly reduced, the damaged DNA might be more accessible to repair enzymes because of histone H2B hyper(ADP-ribosyl)ation. 

Niedergang C, Ittel ME, de Murcia G, Pouyet J, Mandel P (1985) Kinetics of nucleosomal histone HI hyper (ADP-ribosyl)ation and polynucleosomes relaxation. This volume... 

Gaudreau A, Menard L, de Murcia G, Poirier GG (submitted) Differential turnover of poly (ADP-ribosyl)ated proteins on polynucleosomes by poly (ADP-ribose) gly cohydrolase... 

Poly(ADP-Ribose) Glycohydrolase Activity Causes Recondensation of Relaxed Poly(ADP-Ribosyl)ated Polynucleosomes... 

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