Molecular Biology

Keeping One's Identity

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Science  14 Nov 2008:
Vol. 322, Issue 5904, pp. 1026-1027
DOI: 10.1126/science.322.5904.1026c

The phenotype of a cell is in part defined by its pattern of active versus inactive gene expression. During development, progenitor cells divide and differentiate down specific lineages, and daughter cells retain the same activity profile as the cell from which they were derived. It is necessary to preserve these markers of cell identity through mitosis, when transcription ceases and many chromatin-binding proteins that determine gene activity dissociate from the DNA. Most of the chromatin becomes tightly compacted, but some active regions remain open, due to the binding of specific factors to gene promoters. This enables transcription to resume more easily after cell division and is known as gene bookmarking, being analogous to the way a bookmark allows one to open a book at a specific page; gene-specific bookmarking factors have been identified. TATA-binding protein (TBP) is an essential basal transcription factor, which remains bound to active promoters during mitosis, and Xing et al. show that TBP acts as a general bookmarking factor by recruiting the phosphatase PP2A. This enzyme inactivates condensin, which is a large protein complex involved in compacting chromosomes during mitosis. Understanding general mechanisms of bookmarking could be important for controlling cellular behavior during reprogramming, when differentiated cells need to be wiped clean of their previous identity. — HP*

Nat. Cell Biol. 10, 1318 (2008).

  • *Helen Pickersgill is a locum editor in Science's editorial department.

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