The linker histone H1 binds to the short stretches of DNA that link individual nucleosomes and, thereby, establishes and stabilises the chromatin fibre. Similar to other histones, histone H1 can be modified by phosphorylation, methylation, acetylation and ADP-ribosylation. But the connection between this ‘histone H1 code’ and the epigenetic regulation, chromatin structure and function has remained poorly understood. Robert Schneider and colleagues (page ) now demonstrate that phosphorylation of histone H1.4 on S27 by Aurora B kinase has an important regulatory role in these processes. The authors identify H1.4 as a new mitotic marker and show that levels of S27 phosphorylation are highest during metaphase. Phosphorylated H1.4 binds to mitotic chromatin with an affinity that is higher than that of the unphosphorylated form, suggesting a role for S27 phosphorylation in H1.4 mobility and chromatin binding. Previously, Schneider and colleagues showed that S27 phosphorylation prevents binding of heterochromatin protein 1 to H1.4 dimethylated on K26, thereby, potentially linking phosphorylation to gene silencing and centromeric cohesion. Here, they now provide additional evidence for crosstalk between these two modification sites: dimethylation on K26 results in twofold greater phosphorylation of S27.
