The mitotic chromosome is an assembly of rigid elastic axes organized by structural maintenance of chromosomes (SMC) proteins and surrounded by a soft chromatin envelope.
The structure of mitotic chromosomes is still poorly understood. Here we describe the use of a novel approach based on elasticity measurements of a single chromosome for studying the organization of these objects. The data reveal that mitotic chromosomes exhibit a non-homogenous structure consisting of rigid elastic axes surrounded by a soft chromatin envelope. The chemical continuity of DNA, but not RNA, was required for the maintenance of these axes. The axes show a modular structure, and the structural maintenance of chromosomes (SMC) proteins participate in their organization. Topoisomerase II was not involved in either the organization of the axes or the maintenance of the mitotic chromosomes. A model for the assembly and the structure of the mitotic chromosome is proposed. According this model, the chromosome axes are dynamic structures that assemble at the onset and disassemble the end of mitosis, respectively. The SMC proteins, in addition to maintaining axis elasticity, are essential for the determination of the rod-like chromosome shape. The extreme compaction of mitotic chromosomes is determined mainly by the high amount of bivalent ions bound to DNA at mitosis.
Almagro
Sébastien
S
Laboratoire de Biologie Moléculaire et Cellulaire de la Différenciation, INSERM U309, Institut Albert Bonniot, Domaine de la Merci, 38706 La Tronche, France.
Riveline
Daniel
D
Hirano
Tatsuya
T
Houchmandzadeh
Bahram
B
Dimitrov
Stefan
S
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism / Q000502:physiology*; D002875:Chromosomes / Q000378:metabolism / Q000648:ultrastructure; D004247:DNA / Q000737:chemistry; D004250:DNA Topoisomerases, Type II / Q000737:chemistry; D007477:Ions; D008297:Male; D008938:Mitosis; D008954:Models, Biological; D012313:RNA / Q000737:chemistry; D013094:Spermatozoa / Q000378:metabolism / Q000648:ultrastructure; D013997:Time Factors; D014981:Xenopus; D000098550:Structural Maintenance of Chromosome Protein 1
D018797:Cell Cycle Proteins; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D007477:Ions; D000098550:Structural Maintenance of Chromosome Protein 1; D012313:RNA; D004247:DNA; D004250:DNA Topoisomerases, Type II