8.4 The organisation of the mitotic chromosome
In order to prepare the chromosome for mitosis, a process in which DNA molecules become physically separated, an additional stage of compaction occurs to reach the highest level. The processes involved in this final stage of compaction are not clearly understood, but can be represented diagrammatically as in Figure 43. The process probably involves the coiling together of scaffolds into the higher-order structure.
The H1 histone undergoes modification via phosphorylation, which appears to facilitate this further compaction. This additional level of compaction may represent a protective process to prevent physical shearing of the DNA chain within individual chromosomes during mitosis.