“…This steady-state centromeric occupancy is the result of continuous dynamic exchange, on a timescale of several minutes, with a large nuclear pool of free Scm3 molecules. Such exchange was also observed by Luconi et al (2011) in anaphase, although authors did not reliably observe Scm3 in other stages of the cell cycle. Scm3 may dissociate stochastically, and re-associate onto centromeres through interactions with Ndc10 and AT-rich CEN DNA (Xiao et al, 2011; Cho and Harrison, 2011a).…”
Section: Discussionmentioning
confidence: 93%
“…Scm3 may dissociate stochastically, and re-associate onto centromeres through interactions with Ndc10 and AT-rich CEN DNA (Xiao et al, 2011; Cho and Harrison, 2011a). This dynamic property explains the lack of Scm3 in biochemical purifications of kinetochores (Westermann et al, 2003; Akiyoshi et al, 2009), its absence as a stable component of reconstituted Cse4 octasome (Dechassa et al, 2011) and fluctuations in measurements of Scm3 occupancy by ChIP (Luconi et al, 2011; Mishra et al, 2011; Shivaraju et al, 2011; Xiao et al, 2011). As a Cse4-specific histone chaperone, Scm3 needs not, in principle, be retained at centromeres once assembly of the centromeric nucleosome has been accomplished in S phase.…”
The budding yeast centromere contains Cse4, a specialized histone H3 variant. Fluorescence pulse-chase analysis of an internally tagged Cse4 reveals that it is replaced with newly synthesized molecules in S phase, remaining stably associated with centromeres thereafter. In contrast, C-terminally-tagged Cse4 is functionally impaired, showing slow cell growth, cell lethality at elevated temperatures, and extra-centromeric nuclear accumulation. Recent studies using such strains gave conflicting findings regarding the centromeric abundance and cell cycle dynamics of Cse4. Our findings indicate that internally tagged Cse4 is a better reporter of the biology of this histone variant. Furthermore, the size of centromeric Cse4 clusters was precisely mapped with a new 3D-PALM method, revealing substantial compaction during anaphase. Cse4-specific chaperone Scm3 displays steady-state, stoichiometric co-localization with Cse4 at centromeres throughout the cell cycle, while undergoing exchange with a nuclear pool. These findings suggest that a stable Cse4 nucleosome is maintained by dynamic chaperone-in-residence Scm3.DOI:
http://dx.doi.org/10.7554/eLife.02203.001
“…This steady-state centromeric occupancy is the result of continuous dynamic exchange, on a timescale of several minutes, with a large nuclear pool of free Scm3 molecules. Such exchange was also observed by Luconi et al (2011) in anaphase, although authors did not reliably observe Scm3 in other stages of the cell cycle. Scm3 may dissociate stochastically, and re-associate onto centromeres through interactions with Ndc10 and AT-rich CEN DNA (Xiao et al, 2011; Cho and Harrison, 2011a).…”
Section: Discussionmentioning
confidence: 93%
“…Scm3 may dissociate stochastically, and re-associate onto centromeres through interactions with Ndc10 and AT-rich CEN DNA (Xiao et al, 2011; Cho and Harrison, 2011a). This dynamic property explains the lack of Scm3 in biochemical purifications of kinetochores (Westermann et al, 2003; Akiyoshi et al, 2009), its absence as a stable component of reconstituted Cse4 octasome (Dechassa et al, 2011) and fluctuations in measurements of Scm3 occupancy by ChIP (Luconi et al, 2011; Mishra et al, 2011; Shivaraju et al, 2011; Xiao et al, 2011). As a Cse4-specific histone chaperone, Scm3 needs not, in principle, be retained at centromeres once assembly of the centromeric nucleosome has been accomplished in S phase.…”
The budding yeast centromere contains Cse4, a specialized histone H3 variant. Fluorescence pulse-chase analysis of an internally tagged Cse4 reveals that it is replaced with newly synthesized molecules in S phase, remaining stably associated with centromeres thereafter. In contrast, C-terminally-tagged Cse4 is functionally impaired, showing slow cell growth, cell lethality at elevated temperatures, and extra-centromeric nuclear accumulation. Recent studies using such strains gave conflicting findings regarding the centromeric abundance and cell cycle dynamics of Cse4. Our findings indicate that internally tagged Cse4 is a better reporter of the biology of this histone variant. Furthermore, the size of centromeric Cse4 clusters was precisely mapped with a new 3D-PALM method, revealing substantial compaction during anaphase. Cse4-specific chaperone Scm3 displays steady-state, stoichiometric co-localization with Cse4 at centromeres throughout the cell cycle, while undergoing exchange with a nuclear pool. These findings suggest that a stable Cse4 nucleosome is maintained by dynamic chaperone-in-residence Scm3.DOI:
http://dx.doi.org/10.7554/eLife.02203.001
“…In this case, the increase is observed during anaphase and is believed to be accompanied by a structural change in CenH3 nucleosomes. An octasome with two copies of CenH3 lacking Scm3 has been proposed to be present at the centromere during anaphase and a hemisome with one CenH3 copy and Scm3 outside anaphase, although not without conflicting evidence (Luconi et al, 2011;Xiao et al, 2011). Similarly, in human cells, a transition between CenH3 octasomes and hemisomes has been proposed to correlate with absence and presence of the Scm3 homolog HJURP, respectively (Bui et al, 2012).…”
SummaryCentromeres are specified epigenetically in animal cells. Therefore, faithful chromosome inheritance requires accurate maintenance of epigenetic centromere marks during progression through the cell cycle. Clarification of the mechanisms that control centromere protein behavior during the cell cycle should profit from the relatively simple protein composition of Drosophila centromeres. Thus we have analyzed the dynamics of the three key players Cid/Cenp-A, Cenp-C and Cal1 in S2R+ cells using quantitative microscopy and fluorescence recovery after photobleaching, in combination with novel fluorescent cell cycle markers. As revealed by the observed protein abundances and mobilities, centromeres proceed through at least five distinct states during the cell cycle, distinguished in part by unexpected Cid behavior. In addition to the predominant Cid loading onto centromeres during G1, a considerable but transient increase was detected during early mitosis. A low level of Cid loading was detected in late S and G2, starting at the reported time of centromere DNA replication. Our results reveal the complexities of Drosophila centromere protein dynamics and its intricate coordination with cell cycle progression.
“…First, Scm3 is a Cse4 histone chaperone (Shivaraju et al 2011; Stoler et al 2007), which dissociates from the kinetochore during mitotic exit (Luconi et al 2011). Similar behavior has been observed for the fission yeast and human orthologs of Scm3 (Dunleavy et al 2009; Pidoux et al 2009).…”
Section: An Altered Composition Of the Budding Yeast Cenh3 Nucleosome?mentioning
The centromere is a defining feature of the eukaryotic chromosome, required for attachment to spindle microtubules and segregation to the poles at both mitosis and meiosis. The fundamental unit of centromere identity is the centromere-specific nucleosome, in which the centromeric histone 3 (cenH3) variant takes the place of H3. The structure of the cenH3 nucleosome has been the subject of controversy, as mutually exclusive models have been proposed, including conventional and unconventional left-handed octamers (octasomes), hexamers with non-histone protein constituents, and right-handed heterotypic tetramers (hemisomes). Hemisomes have been isolated from native centromeric chromatin, but traditional nucleosome assembly protocols have generally yielded partially unwrapped left-handed octameric nucleosomes. In budding yeast, topology analysis and high-resolution mapping has revealed that a single right-handed cenH3 hemisome occupies the ~80-bp Centromere DNA Element II (CDEII) of each chromosome. Overproduction of cenH3 leads to promiscuous low-level incorporation of octasome-sized particles throughout the yeast genome. We propose that the right-handed cenH3 hemisome is the universal unit of centromeric chromatin, and that the inherent instability of partially unwrapped left-handed cenH3 octamers is an adaptation to prevent formation of neocentromeres on chromosome arms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.