How transcription helps to maintain centromere identity
Replication and transcription of genomic DNA requires partial disassembly of nucleosomes to allow progression of polymerases. This constitutes both an opportunity to remodel the underlying chromatin as well as the potential danger of losing epigenetic information. Centromeric transcription has been shown to be required for stable incorporation of the centromere-specific histone dCENP-A in M/G1-phase, which depends on the eviction of previously deposited H3/H3.3-placeholder nucleosomes. Interestingly, we find that the histone chaperone and transcription elongation factor Spt6 spatially and temporarily coincides with centromeric transcription and prevents the loss of old CENP-A nucleosomes in both Drosophila and human cells. Spt6 binds directly to dCENP-A and shows enhanced association with non-phosphorylatable dCENP-A mutants compared to histone H3, while phosphomimetic residues alleviate association with Spt6. We propose that Spt6 acts as a conserved CENP-A maintenance factor, which is required during transcription-mediated chromatin remodelling at the centromere to ensure long-term stability of epigenetic centromere identity.
Senior Researcher, Wellcome Centre for Cell Biology, University of Edinburgh