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During mitosis it is believed that constitutive heterochromatin is necessary for proper segregation of sister chromatids and centromere function. [6] The repeat sequences found at the pericentromeres are not conserved throughout many species and depend more on epigenetic modifications for regulation, while telomeres show more conserved sequences.
All cells of a given species package the same regions of DNA in constitutive heterochromatin, and thus in all cells, any genes contained within the constitutive heterochromatin will be poorly expressed. For example, all human chromosomes 1, 9, 16, and the Y-chromosome contain large regions of constitutive heterochromatin. In most organisms ...
[55] [56] Specific remodeler depletion results in activation of proliferative genes through a failure to maintain silencing. [50] Some remodelers act on enhancer regions of genes rather than the specific loci to prevent re-entry into the cell cycle by forming regions of dense heterochromatin around regulatory regions. [56]
Establishment of sister chromatid cohesion is the process by which chromatin-associated cohesin protein becomes competent to physically bind together the sister chromatids. In general, cohesion is established during S phase as DNA is replicated, and is lost when chromosomes segregate during mitosis and meiosis.
Function [ edit ] CENPA is a protein which epigenetically defines the position of the centromere on each chromosome, [ 7 ] determining the position of kinetochore assembly and the final site of sister chromatid cohesion during mitosis .
By contrast, CMT2 and CMT3 preferentially function in constitutive heterochromatin and depend strongly on DDM1 to maintain silencing over these regions. [ 131 ] [ 5 ] [ 3 ] Similarly, MET1, which maintains DNA methylation at CG sites after replication, requires DDM1 to access heterochromatin and maintain CG methylation in those regions. [ 132 ]
The family of heterochromatin protein 1 (HP1) ("Chromobox Homolog", CBX) consists of highly conserved proteins, which have important functions in the cell nucleus.These functions include gene repression by heterochromatin formation, transcriptional activation, regulation of binding of cohesion complexes to centromeres, sequestration of genes to the nuclear periphery, transcriptional arrest ...
Chromosome segregation is the process in eukaryotes by which two sister chromatids formed as a consequence of DNA replication, or paired homologous chromosomes, separate from each other and migrate to opposite poles of the nucleus. This segregation process occurs during both mitosis and meiosis. Chromosome segregation also occurs in prokaryotes ...