Abstract
Centromeres define the chromosomal position where kinetochores form to link the chromosome to microtubules during mitosis and meiosis. Centromere identity is determined by incorporation of a specific histone H3 variant termed CenH3. As for other histones, escort and deposition of CenH3 must be ensured by histone chaperones, which handle the non-nucleosomal CenH3 pool and replenish CenH3 chromatin in dividing cells. Here, we show that the Arabidopsis orthologue of the mammalian NUCLEAR AUTOANTIGENIC SPERM PROTEIN (NASP) and Schizosaccharomyces pombe histone chaperone Sim3 is a soluble nuclear protein that binds the histone variant CenH3 and affects its abundance at the centromeres. NASPSIM3 is co-expressed with Arabidopsis CenH3 in dividing cells and binds directly to both the N-terminal tail and the histone fold domain of non-nucleosomal CenH3. Reduced NASPSIM3 expression negatively affects CenH3 deposition, identifying NASPSIM3 as a CenH3 histone chaperone.
Highlights
Eukaryotic DNA is organized into chromatin using histones as components of its building blocks, the nucleosomes
In four independent gCenH3ÀEYFP mass spectrometry samples we identified between six and 14 peptides that corresponded to NASPSIM3 (AT4G37210) and which were not detected in the EYFP control samples (Figures 1a and S1a)
52 peptides matching NASPSIM3 with a combined coverage of 41.06% were detected, strongly suggesting that NASPSIM3 can be found in a complex with CenH3 in vivo
Summary
Eukaryotic DNA is organized into chromatin using histones as components of its building blocks, the nucleosomes. Deposition and eviction of the different histone variants depend on histone chaperones that play an important role in defining discrete chromatin landscapes important for genome function, stability and cell identity (Hammond et al, 2017). These different histone chaperones, defined ‘as factors that associate with histones and stimulate a reaction involving histone transfer without being part of the final product’ (De Koning et al, 2007), execute distinct functions in an interaction network, which has been extensively characterized in animals and yeast. 22 and 25 genes encoding histone chaperones in Arabidopsis and rice, respectively, have been identified (Tripathi et al, 2015)
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