Introduction 2001 1998 strictly 2002 1994 1985 1986 2005 1998 2001 Cercopithecus aethiops 1979 1982 1979 1983 1984 1983 1983 1986 1986 1983 Lytechinus variegatus 1996 2006 2005 1989 2001 1996 1996 1996 1993 2004 2002 1998 2004 1982 Eco Material and methods Preparation of DNA C. aethiops Eco 1975 Eco 1975 Eco Escherichia Coli Eco 1996 1985 Ava Pst Not Xho Pst Xba Chromatin reconstitution Xenopus laevis 2003 1999 2005 Nucleosome arrays with 172-α7 and mononucleosomes with 172-α2 were reconstituted by the salt dialysis method. Octamers were mixed with the DNA in 10 mM Tris–HCl, pH 7.5; 2 M NaCl and kept at 30°C for 30 min. The mixture was transferred to mini dialysis tubes (Pierce, Rockford, USA) and dialysed against buffers with stepwise decreasing NaCl concentrations at 4°C (1.8, 1.4, 1.0, 0.8, 0.6, 0.4, 0.2 and 0.1 M for 1 h each and 0.005 M over night). The reconstitutions took place at different weight ratios of histone-octamer to DNA, ranging between values of 0.3–1.0. The DNA mass was 0.02 μg/μl. Eco 2 Eco Eco Eco Atomic force microscopy 2005 Image analysis Atomic force microscopy images were flattened and zooms of individual complexes were produced using the Nanoscope IIIa software (version 5.12r3, Veeco Instruments). Measurements of nucleosomal heights were done with the section analysis tool available in the same software package. This was also used to decide in some critical cases, whether a pair of two closely localised nucleosomes or a single one was present. When the cross-section showed two peaks or clearly a plateau next to a peak, two closely localised nucleosomes were assumed. L complex L free 1 \documentclass[12pt]{minimal}
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$$ L_{{{\text{free}}}} = L_{{{\text{complex}}}} - n_{{{\text{ncp}}}} \cdot 11\,{\text{nm,}} $$\end{document} n ncp cc cc cc cc cc Results We studied the positioning of reconstituted nucleosomes on AGM α -satellite (AS) tandemly repeated DNA. The cloned AGM AS 1 1 1 2 1986 Hin 1982 1986 1983 Not Xho 1 Fig. 1 a 1 upper case letters 2 1986 Lower case letters Eco underlined 1978 The sequence in brackets Eco n n b Not Xho lane 1 lane 2 Not Xho n  Fig. 2 Eco a First two lanes b a. Arrows c Eco lane 1 lane 2 Eco d lane 2 c  1 Gel electrophoretic characterisation of chromatin reconstituted with 172-α7 2 1983 2 Eco Eco 1982 1986 1983 2 2 Eco 2 Eco 2 2 Eco 1982 1986 1983 2 Eco AFM imaging of 172-α7 nucleosome arrays L. variegatus 1998 1985 1993 2004 2004 2002 2003 3 3 3 2 3 3 2005 Fig. 3 a i a b g b c d e 2 f g arrows h i k n ncp Blue closed symbols continuous line blue open symbols dashed line green red 2 Error bars  1996 2005 L ncp 3 2+ 3 n ncp L free n ncp L ncp 2 cc 4 2002 n ncp-av cc 4 4 Fig. 4 cc a cc n ncp-av b cc n ncp n ncp-av c cc n ncp-av Numbers and arrow heads cc a b c a Error bars  1998 1991 2002 4 n ncp-av 4 cc 4 cc 4 3 2004 2004 2002 L ncp cc cc exp L mono 2 \documentclass[12pt]{minimal}
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$$ cc_{{{\text{exp}}}} = L_{{{\text{mono}}}} - L_{{{\text{ncp}}}} + 11\,{\text{nm}} + (a \cdot L_{{{\text{mono}}}} ), a = 0,\,1,\,2... $$\end{document} a x 4 cc 1991 AFM imaging of 172-α2 mononucleosomes 5 5 Fig. 5 a b e f g L ncp white bars black bars L ncp 3  5 2005 5 L ncp 2003 L ncp L ncp 5 P r 2003 r 6 r r- Eco 1 r Eco Eco Fig. 6 r r white bars r r  Discussion Nucleosomal positioning along repetitive AGM AS We reconstituted nucleosomes with dimers (172-α2) and heptamers (172-α7) of repetitive AGM AS by the salt dialysis method. Enzymatic digestions and atomic force microscopy were used to characterise the nucleosomal organisation along this DNA. The results demonstrate the formation of a well-defined (sequence-dependent) nucleosomal arrangement, essentially similar to the 5S rDNA model system. In the AGM AS arrays, however, the variation in the separation between neighbouring nucleosomes was rather large, and evenly spaced nucleosomes occurred only to a limited extent. 1982 Eco 1982 1986 1983 1982 1983 1982 cc cc 1998 cc 2+ 2004 cc 2004 2002 cc 2002 1995 1996 1997 cc cc cc 4 cc 4 cc Eco 1986 1983 Eco Eco 6 2004 Eco 1986 Relevance of AGM AS for centromeric chromatin structures 2005 1996 1982 1983 2005 1998 1997