In eukaryotes, kinetochore assembly takes place on the centromere. The histone H3 variant CENP-A is important for this process and for maintenance of centromere epigenetic identity. In addition, the centromeric alpha-satellite DNA contains a specific set of post-translational modifications and is transcribed at low levels. Removing the H3K4 dimethylation mark on kinetochore chromatin results in a decrease in transcription and prevents the loading of CENP-A, thereby disrupting kinetochores. But is it the chromatin environment or the level of transcription that is important for CENP-A recruitment? By using human artificial chromosome rich in alpha-satellite sequences, Bill Earnshaw and co-workers (p. 411) provide an answer to this question. They show that the C-terminal transactivation domains from the NF-κB p65 subunit and the herpes virus VP16 upregulate H3K9 acetylation to a similar level, and increase transcription ~10- and ~150-fold, respectively. The changes induced by p65 do not affect kinetochore structure or function. By contrast, the greater increase in transcriptional activity induced by VP16 is accompanied by a loss of pre-assembled CENP-A from the kinetochore as well as defective CENP-A loading. From these results, the authors conclude that transcriptional activity from centromeric chromatin has to be carefully balanced to maintain kinetochore integrity.

© 2012.
2012