Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.
Histone modifications have been associated with particular states of transcriptional activity and are thought to serve as an "information code". However, this principle does not apply to histone phosphorylation, which can be detected in two, seemingly contrasting situations, i.e., in a transcriptionally hyperactive state following growth factor stimulation and in transcriptionally paused mitotic chromosomes. There are several indications that mitotic phosphorylation of histone H3 at serine-10 by the Aurora B kinase and trimethylation at lysine-9 by the methyl transferase Suvar3,9 operate as a "binary switch", which determines recruitment or eviction of heterochromatin-specific proteins from pericentromeric repeats. Moreover, threonine-3 phosphorylation of histone H3 by the newly identified haspin kinase seems to promote chromatid cohesion during mitosis. We discuss here emerging information and new ideas suggesting that these modifications, in combination to upstream and downstream marks, constitute a system of intrinsic folding determinants that facilitate chromatin condensation and confer topological specificity to mitotic chromosomes.