Chromosome scaffold

Source: Wikipedia, the free encyclopedia.

In

eukaryotic chromosomes throughout the cell cycle. These scaffold proteins are responsible for the condensation of chromatin during mitosis.[1]

Origin

In the late 1970s,

chromosomes after they depleted the histone proteins. This backbone was localized along the chromosome axis, and was termed the ‘chromosome scaffold’.[2][1]

Proteins of the scaffold

Immunodetection of a chromosome showing DNA (blue) and two scaffold proteins: SMC2 (red) and topoisomerase IIα (green)[1]

In

histones) bind the chromatin fiber around themselves forming a long, continuous axis or backbone that gives the chromosomes their shape. For this reason they are known as the ‘scaffold’ of chromosomes.[1]

Three protein groups have been identified as the main components of the scaffold: DNA topoisomerase IIα, condensins, and the KIF4A kinesin. When these proteins are removed, the chromosome shape does not appear and the chromatin fibers spread out.[1]

Topoisomerase IIα

The enzyme DNA topoisomerase IIα prominently appears along the chromosome axis as part of the scaffold.[3] In mitosis, it is concentrated at the centromeres and the axis along the chromosome arms. It is thought that the protein has a role in untangling the DNA as the loops become more concentrated along the axis during the condensation of the chromosomes.[4] The removal of this protein causes a dramatic loss of the chromosome structure in mitosis, and the cell cycle comes to a stop.[5]

SMC family proteins

TADs to an array of loops around the chromosome axis. Condensin II drives the compaction of the chromosome loops along the axis.[4]

In particular, SMC2 (present in condensin I and II) is detected in the interior of the chromosome as part of the scaffold.[4] When SMC2 is inhibited, the structure of the mitotic chromosome suffers grave defects.[7]

KIF4

KIF4A, a chromokinesin, is implicated in the shaping of chromosomes during mitosis. It binds to condensin I through the CAP-G subunit. It is known that KIF4A regulates the behavior of condensin I, because in absence of KIF4A the chromosome axis does not become enriched with condensin I.[8]

References

  1. ^
    PMID 26132639
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  2. S2CID 40355379
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  3. PMID 2985625
    .
  4. ^
    ISBN 978-0-323-34126-4
    .
  5. PMID 32414923
    .
  6. S2CID 23908801
    .
  7. PMID 14532007
    .
  8. PMID 27633014
    .
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