What is "bookmarking"

vb. (present participle of bookmark English)

Bookmarking (also "gene bookmarking" or "mitotic bookmarking") refers to a potential mechanism of transmission of gene expression programs through cell division.

During mitosis, gene transcription is silenced and most transcription factors are removed from chromatin. The term bookmarking compares transcription to reading from a book. The pause in transcription during mitosis is like closing the book. "Molecular bookmarks" are the factors that allow transcription to resume in an orderly fashion in newborn cells following mitosis (when the book is re-opened).

Bookmarks fulfill the following criteria:

• at some point prior to the onset of mitosis, the promoters of genes that exist in a transcription-competent state become "marked" in some way,
• this "mark" persists both during and after mitosis, and
• the marking transmits gene expression memory by preventing the mitotic compaction of DNA at this locus, or by facilitating reassembly of transcription complexes on the promoter, or both.