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Bioessays. 2014 Jun;36(6):591-7. doi: 10.1002/bies.201400021. Epub 2014 Apr 6.

A new light on DNA replication from the inactive X chromosome.

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Developmental Therapeutic Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, USA.


While large portions of the mammalian genome are known to replicate sequentially in a distinct, tissue-specific order, recent studies suggest that the inactive X chromosome is duplicated rapidly via random, synchronous DNA synthesis at numerous adjacent regions. The rapid duplication of the inactive X chromosome was observed in high-resolution studies visualizing DNA replication patterns in the nucleus, and by allele-specific DNA sequencing studies measuring the extent of DNA synthesis. These studies conclude that inactive X chromosomes complete replication earlier than previously thought and suggest that the strict order of DNA replication detected in the majority of genomic regions is not preserved in non-transcribed, "silent" chromatin. These observations alter current concepts about the regulation of DNA replication in non-transcribed portions of the genome in general and in the inactive X-chromosome in particular.


DNA replication; cell cycle; chromatin; epigenetics; inactive X chromosome

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