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Molecular c ell Biology observed in extracts from Increased levels of acetylated Smc3 were deacetylase genes deleted, for acetylated Smc3. strains, each of which had one of the 11 known and Beckouët chromatid cohesion. deacetylation cycle in establishing sister an important role for the Smc3 acetylation– Smc3 in identify Hos1 as the enzyme that deacetylates responsible, were unknown. Two groups now the importance of this, and the deacetylase (Eco1). Smc3 is deacetylated at anaphase, but the acetyltransferase establishment of cohesion 1 cohesion depends on the acetylation of Smc3 by separation in mitosis, and the establishment of from their replication in S cohesion 1 (Scc1 chromosomes of which are structural maintenance of The cohesin complex, the core components it is effective in the presence of Hos1 and active reconstituted Smc3 deacetylation and found that To cleavage is necessary to trigger deacetylation. deacetylation. These data suggest that Scc1 virus protease is expressed undergo Smc3 variant that is cleaved when the tobacco etch deacetylation, whereas cells expressing a Scc1 cannot be cleaved by separase prevents Smc3 segregation. Expression of a Scc1 variant that from chromosomes to trigger chromosome cleaved by separase, which releases cohesin anaphase? At the onset of anaphase Scc1 is indicating that Hos1 is the Smc3 deacetylase. (which do not normally have acetylated Smc3), various conditions, including in G1‑arrested cells Cycling through acetylation
confirm this So, why is Smc3 deacetylation triggered at To identify the Smc3 deacetylase, Borges
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et al M 1 (Smc1), Smc3 and sister chromatid y in vitro a ) E L C c , holds sister chromatids together m . screened 11 i l l a n Beckouët
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t s r e . s e r v e d and thus efficient cohesion, in the next cell available for ensure that there is a pool of unacetylated Smc3 has been released from the chromosomes, to deacetylates Smc3 at anaphase, after cohesin during S Smc3 that is essential for establishing cohesion that it is the for reduced Eco1 function. These data suggest levels of acetylated Smc3, does not compensate that depletion of rescue cohesion defects. Borges the absence of Eco1 and Hos1, acetylated Smc3 persists in the next cell cycle in the presence of Hos1, as expected. Although acetylated Smc3 from the previous cell cycle in defects and that these cells inherit little or no found that depletion of Eco1 causes cohesion separase. Borges a t version of Eco1 that can be depleted from cells in To enables Smc3 deacetylation. dissociation from chromosomes at anaphase it is bound to chromosomes and that its complex is protected from deacetylation when but not cohesin. This suggests that the cohesin of a nuclease that fragments chromosomal DNA deacetylation also occurs SMC proteins in action. FURTHER READING 39 essential for establishment of sister chromatid cohesion. 39 deacetylates Smc3 to close the cohesin acetylation cycle. ORIGINAL RESEARCH PAPER
emperature investigate this, both groups expressed a In short, these papers show that Hos1 But why is Smc3 deacetylation important? , 689–699 (2010) , 677–688 (2010) | Beckouët, F. R
phase. ch highlights de novo de novo ‑ sensitive manner. Beckouët
Hirano, T. At the heart of the chromosome: et al Hos1 Nature Rev. Mol. Cell Biol.
v acetylation of unacetylated Eco1‑mediated acetylation, olume 11 . showed that Smc3 , which results in increased S et al Borges, V. in vitro . An Smc3 acetylation cycle is Katharine H.
this does not et al | et november in the presence
al . Hos1 7 , 311–322 (2006) . also show Mol. Cell
Wrighton Mol. Cell
et al cycle.
2010
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