17:
241:
252:
is no linear relationship between the length of the linker DNA and the dimensions (instead there are two distinct classes). There is also data from experiments which cross-linked nucleosomes that shows a two-start structure. There is evidence that suggests both the solenoid and zig-zag (two-start) structures are present in 30 nm fibres. It is possible that chromatin structure may not be as ordered as previously thought, or that the 30 nm fibre may not even be present
122:. In the solenoid structure, the nucleosomes fold up and are stacked, forming a helix. They are connected by bent linker DNA which positions sequential nucleosomes adjacent to one another in the helix. The nucleosomes are positioned with the histone H1 proteins facing toward the centre where they form a
251:
Even the more recent research produces conflicting information. There is data from electron microscopy measurements of the 30 nm fibre dimensions that has physical constraints which mean it can only be modelled with a one-start helical structure like the solenoid structure. It also shows there
206:
The histone H4 tail is essential for formation of 30 nm fibres. However, acetylation of core histone tails affects the folding of chromatin by destabilising interactions between the DNA and the nucleosomes, making histone modulation a key factor in solenoid structure. Acetylation of H4K16 (the
202:
There is an acidic patch on the surface of histone H2A and histone H2B proteins which interacts with the tails of histone H4 proteins in adjacent nucleosomes. These interactions are important for solenoid formation. Histone variants can affect solenoid formation, for example H2A.Z is a histone
134:
Finch and Klug's electron microscopy images had a lack of visible detail so they were unable to determine helical parameters other than the pitch. More recent electron microscopy images have been able to define the dimensions of solenoid structures and identified it as a left-handed helix. The
279:. This structure, like the two-start twisted-ribbon model, involves alternating nucleosomes stacking to form two parallel helices, but the nucleosomes are on opposite sides of the helices with the linker DNA crossing across the centre of the helical axis.
130:
angles of 11 nm, which is about the same diameter as a nucleosome. There are approximately 6 nucleosomes in each turn of the helix. Finch and Klug actually observed a wide range of nucleosomes per turn but they put this down to flattening.
266:
The two-start twisted-ribbon model was proposed in 1981 by Worcel, Strogatz and Riley. This structure involves alternating nucleosomes stacking to form two parallel helices, with the linker DNA zig-zagging up and down the helical axis.
231:
attaching to a central scaffolding matrix in the nucleus creating loops of solenoid chromatin between 4.5 and 112 kilobase pairs long. The central scaffolding matrix itself forms a spiral shape for an additional layer of compaction.
151:, whilst the DNA in one human cell would stretch to just over 2 metres long if it were unwound. The "beads on a string" structure can compact DNA to 7 times smaller. The solenoid structure can increase this to be 40 times smaller.
226:
Chromatin can form a tertiary chromatin structure and be compacted even further than the solenoid structure by forming supercoils which have a diameter of around 700 nm. This supercoil is formed by regions of DNA called
114:
proteins. The primary chromatin structure, the least-packed form, is the 11 nm, or βbeads on a stringβ form, where DNA is wrapped around nucleosomes at relatively regular intervals, as Roger
Kornberg proposed.
1113:
391:
180:
There are many factors that affect whether the solenoid structure will form or not. Some factors alter the structure of the 30 nm fibre, and some prevent it from forming in that region altogether.
601:
Walter, Peter; Roberts, Keith; Raff, Martin; Lewis, Julian; Johnson, Alexander; Alberts, Bruce (2002). Bruce
Alberts; Alexander Johnson; Julian Lewis; Martin Raff; Keith Roberts; Peter Walter (eds.).
287:
The superbead model was proposed by Renz in 1977. This structure is not helical like the other models, it instead consists of discrete globular structures along the chromatin which vary in size.
631:
Zhou, Jiansheng; Fan, Jun Y; Rangasamy, Danny; Tremethick, David J (28 October 2007). "The nucleosome surface regulates chromatin compaction and couples it with transcriptional repression".
203:
variant of H2A, and it has a more acidic patch than the one on H2A, so H2A.Z would have a stronger interaction with histone H4 tails and probably contribute to solenoid formation.
118:
Histone H1 protein binds to the site where DNA enters and exits the nucleosome, wrapping 147 base pairs around the histone core and stabilising the nucleosome, this structure is a
143:
The solenoid structure's most obvious function is to help package the DNA so that it is small enough to fit into the nucleus. This is a big task as the nucleus of a
1309:"Differences of supranucleosomal organization in different kinds of chromatin: cell type-specific globular subunits containing different numbers of nucleosomes"
218:
To decompact the 30 nm fibre, for instance to transcriptionally activate it, both H4K16 acetylation and removal of the histone H1 proteins are required.
678:"Chromatin structure. Nuclease digestion profiles reflect intermediate stages in the folding of the 30-nm fiber rather than the existence of subunit beads"
1244:
964:
826:
Robinson, Philip J.J.; An, Woojin; Routh, Andrew; Martino, Fabrizio; Chapman, Lynda; Roeder, Robert G.; Rhodes, Daniela (September 2008).
195:
affects the structure of the 30 nm fibre, which is why Finch and Klug were not able to form solenoid structures in the presence of
86:
patterns to determine their model of the structure. This was the first model to be proposed for the structure of the 30 nm fibre.
633:
1025:
891:
612:
248:
Several other models have been proposed and there is still a lot of uncertainty about the structure of the 30 nm fibre.
775:
Shogren-Knaak, M. (10 February 2006). "Histone H4-K16 Acetylation
Controls Chromatin Structure and Protein Interactions".
158:
active in certain areas. It is the secondary chromatin structure that is important for this transcriptional repression as
883:
An introduction to genetic analysis, Chapter 3: Chromosomal Basis of
Heredity, Three-dimensional structure of chromosomes
544:"EM measurements define the dimensions of the "30-nm" chromatin fiber: Evidence for a compact, interdigitated structure"
451:"Involvement of histone H1 in the organization of the nucleosome and of the salt-dependent superstructures of chromatin"
1180:"Chromatin fibers are left-handed double helices with diameter and mass per unit length that depend on linker length"
521:
228:
126:. Finch and Klug determined that the helical structure had only one-start point because they mostly observed small
604:
Molecular
Biology of the Cell, Chapter 4: DNA and Chromosomes, Chromosomal DNA and Its Packaging in the Chromosome
1072:
907:
Dorigo, B. (26 November 2004). "Nucleosome Arrays Reveal the Two-Start
Organization of the Chromatin Fiber".
1178:
Williams, S. P.; Athey, B. D.; Muglia, L. J.; Schappe, R. S.; Gough, A. H.; Langmore, J. P. (January 1986).
299:
is the most condensed form of eukaryotic DNA, it is packaged by protamines rather than nucleosomes, whilst
511:
1417:
1313:
455:
16:
1070:
Fussner, E.; Ching, R. W.; Bazett-Jones, D. P. (January 2011). "Living without 30nm chromatin fibers".
469:
244:
Solenoid model (left) and two-start twisted- ribbon model (right) of 30 nm fibre, showing DNA only.
155:
828:"30 nm Chromatin Fibre Decompaction Requires both H4-K16 Acetylation and Linker Histone Eviction"
1021:"New insights into nucleosome and chromatin structure: an ordered state or a disordered affair?"
464:
1359:
1402:
327:
Kornberg, R. D. (24 May 1974). "Chromatin
Structure: A Repeating Unit of Histones and DNA".
1253:
1193:
1132:
973:
916:
880:
Griffiths, A. J. F.; Miller, J. H.; Suzuki, D. T.; Lewontin, R. C.; Gelbart, W. M. (2000).
784:
555:
400:
338:
8:
1184:
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404:
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827:
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658:
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487:
450:
1284:
1239:
1205:
1155:
1108:
960:"Evidence for heteromorphic chromatin fibers from analysis of nucleosome interactions"
958:
Grigoryev, S. A.; Arya, G.; Correll, S.; Woodcock, C. L.; Schlick, T. (27 July 2009).
694:
423:
386:
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689:
642:
573:
563:
482:
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418:
408:
346:
196:
135:
structure of solenoids are insensitive to changes in the length of the linker DNA.
56:
752:
735:
677:
1364:
350:
64:
1114:
Proceedings of the
National Academy of Sciences of the United States of America
1085:
881:
602:
392:
Proceedings of the
National Academy of Sciences of the United States of America
60:
843:
542:
Robinson, P. J. J.; Fairall, L.; Huynh, V. A. T.; Rhodes, D. (14 April 2006).
1411:
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127:
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240:
1422:
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1005:
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654:
587:
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304:
119:
44:
1344:
1223:
1164:
711:
432:
358:
98:, which are histone octamers formed of core histone proteins; two histone
1403:
Aaron Klug tells his life story at the Web of
Stories: The Solenoid Model
1326:
1293:
1127:
496:
478:
300:
103:
99:
95:
215:
from the N-terminal of histone H4) inhibits 30 nm fibre formation.
1240:"Involvement of histone H1 in the organization of the chromosome fiber"
212:
148:
111:
107:
75:
68:
37:
646:
144:
59:
by using aniline dyes to stain it. In 1974, it was first proposed by
33:
29:
1038:
36:
fibre. It is a secondary chromatin structure which helps to package
189:
1377:
275:
The two-start cross-linker model was proposed in 1986 by Williams
516:(4 ed.). Jones & Bartlett Publishers. pp. 210β252.
254:
192:
160:
123:
154:
When DNA is compacted into the solenoid structure can still be
208:
1019:
Luger, K.; Dechassa, M. L.; Tremethick, D. J. (22 June 2012).
736:"Structure and organization of chromatin fiber in the nucleus"
879:
676:
Walker, P. R.; Sikorska, M.; Whitfield, J. F. (25 May 1986).
296:
276:
165:
957:
185:
1177:
630:
541:
290:
40:
1069:
74:
The solenoid model was first proposed by John Finch and
1018:
886:(7. ed., 1. print. ed.). New York: W. H. Freeman.
675:
1109:"Structure of chromatin and the linking number of DNA"
825:
600:
1106:
449:Thoma, F.; Koller, T.; Klug, A. (1 November 1979).
513:Molecular Biology, Chapter 6: Chromosome Structure
387:"Solenoidal model for superstructure in chromatin"
63:that chromatin was based on a repeating unit of a
768:
261:
1409:
1360:"Packaging paternal chromosomes with protamine"
1245:Proceedings of the National Academy of Sciences
1237:
965:Proceedings of the National Academy of Sciences
548:Proceedings of the National Academy of Sciences
448:
270:
1238:Renz, M.; Nehls, P.; Hozier, J. (1 May 1977).
537:
535:
533:
322:
320:
951:
774:
1300:
1171:
1107:Worcel, A.; Strogatz, S.; Riley, D. (2001).
1063:
530:
444:
442:
380:
378:
376:
374:
372:
370:
368:
317:
20:30 nm chromatin fibre in solenoid structure
1100:
900:
626:
624:
229:scaffold/matrix attachment regions (SMARs)
1351:
1334:
1283:
1265:
1213:
1154:
1144:
1126:
1046:
1012:
995:
985:
851:
751:
734:Li, Guohong; Zhu, Ping (7 October 2015).
693:
669:
634:Nature Structural & Molecular Biology
577:
567:
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384:
1306:
1231:
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723:
721:
439:
365:
326:
239:
15:
875:
873:
871:
621:
291:Some alternative forms of DNA packaging
147:cell has a diameter of approximately 6
32:is a model for the structure of the 30
1410:
906:
169:
1357:
1026:Nature Reviews Molecular Cell Biology
733:
718:
509:
235:
94:DNA in the nucleus is wrapped around
868:
385:Finch, J. T.; Klug, A. (June 1976).
221:
594:
13:
282:
55:Chromatin was first discovered by
14:
1434:
1396:
607:(4th ed.). Garland Science.
503:
1358:Braun, Robert E. (1 May 2001).
819:
682:Journal of Biological Chemistry
1073:Trends in Biochemical Sciences
262:Two-start twisted-ribbon model
1:
1206:10.1016/S0006-3495(86)83637-2
753:10.1016/j.febslet.2015.04.023
695:10.1016/S0021-9258(19)62719-5
310:
170:tertiary chromatin structures
50:
832:Journal of Molecular Biology
351:10.1126/science.184.4139.868
271:Two-start cross-linker model
175:
89:
7:
1314:The Journal of Cell Biology
1307:Zentgraf, H (1 July 1984).
456:The Journal of Cell Biology
295:The chromatin in mammalian
138:
10:
1439:
1086:10.1016/j.tibs.2010.09.002
303:package their DNA through
844:10.1016/j.jmb.2008.04.050
510:Tropp, Burton E. (2012).
987:10.1073/pnas.0903280106
929:10.1126/science.1103124
797:10.1126/science.1124000
569:10.1073/pnas.0601212103
168:are assembled in large
1267:10.1073/pnas.74.5.1879
1146:10.1073/pnas.78.3.1461
746:(20PartA): 2893β2904.
414:10.1073/pnas.73.6.1897
245:
21:
243:
184:The concentration of
19:
1327:10.1083/jcb.99.1.272
479:10.1083/jcb.83.2.403
1258:1977PNAS...74.1879R
1198:1986BpJ....49..233W
1185:Biophysical Journal
1137:1981PNAS...78.1461W
978:2009PNAS..10613317G
972:(32): 13317β13322.
921:2004Sci...306.1571D
915:(5701): 1571β1573.
789:2006Sci...311..844S
560:2006PNAS..103.6506R
405:1976PNAS...73.1897F
343:1974Sci...184..868K
80:electron microscopy
78:in 1976. They used
1418:Molecular genetics
246:
236:Alternative models
211:which is the 16th
110:proteins, and two
22:
893:978-0-7167-3520-5
783:(5762): 844β847.
688:(15): 7044β7051.
641:(11): 1070β1076.
614:978-0-8153-3218-3
554:(17): 6506β6511.
337:(4139): 868β871.
222:Further packaging
156:transcriptionally
84:X-ray diffraction
1430:
1390:
1389:
1355:
1349:
1348:
1338:
1304:
1298:
1297:
1287:
1269:
1252:(5): 1879β1883.
1235:
1229:
1227:
1217:
1175:
1169:
1168:
1158:
1148:
1130:
1128:cond-mat/0007235
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197:chelating agents
57:Walther Flemming
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1365:Nature Genetics
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470:10.1.1.280.4231
447:
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399:(6): 1897β901.
383:
366:
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318:
313:
293:
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283:Superbead model
273:
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188:, particularly
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67:and around 200
65:histone octamer
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1397:External links
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1321:(1): 272β286.
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1033:(7): 436β447.
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28:structure of
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120:chromatosome
117:
106:dimers, two
93:
73:
54:
25:
23:
301:prokaryotes
96:nucleosomes
82:images and
1412:Categories
1080:(1): 1β6.
311:References
213:amino acid
112:histone H4
108:histone H3
76:Aaron Klug
69:base pairs
51:Background
38:eukaryotic
1276:0027-8424
704:0021-9258
465:CiteSeerX
176:Formation
145:mammalian
90:Structure
43:into the
30:chromatin
1386:11326265
1094:20926298
1057:22722606
1006:19651606
945:20869252
937:15567867
862:18653199
813:11079405
805:16469925
762:25913782
663:40546856
655:17965724
588:16617109
190:divalent
139:Function
71:of DNA.
26:solenoid
1345:6736129
1336:2275636
1254:Bibcode
1224:3955173
1215:1329627
1194:Bibcode
1165:6940168
1133:Bibcode
1048:3408961
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