Scm3, an essential Saccharomyces cerevisiae centromere protein required for G ₂ /M progression and Cse4 localization

Abstract

A universal mark of centromeric chromatin is its packaging by a variant of histone H3 known as centromeric H3 (CenH3). The mechanism by which CenH3s are incorporated specifically into centromere DNA or the specialized function they serve there is not known. In a genetic approach to identify factors involved in CenH3 deposition, we screened for dosage suppressors of a temperaturesensitive cse4 allele in Saccharomyces cerevisiae (Cse4 is the S. cerevisiae CenH3). Independent screens yielded ORF YDL139C, which we named SCM3. Dosage suppression by SCM3 was specific for alleles affecting the histone fold domain of Cse4. Copurification and two-hybrid studies showed that Scm3 and Cse4 interact in vivo, and chromatin immunoprecipitation revealed that Scm3, like Cse4, is found associated with centromere DNA. Scm3 contains two essential protein domains, a Leu-rich nuclear export signal and a heptad repeat domain that is widely conserved in fungi. A conditional scm3 allele was generated to allow us to deplete Scm3. Upon Scm3 depletion, cells undergo a Mad2-dependent G 2/M arrest, and centromere localization of Cse4 is perturbed. We suggest that S. cerevisiae Scm3 defines a previously undescribed family of fungal kinetochore proteins important for CenH3 localization.centromeric H3 ͉ chromosome segregation ͉ kinetochore ͉ yeast ͉ CENP-A

Histone chaperones in nucleosome eviction and histone exchange

“…CenH3, the centromeric version of H3, is perhaps the most enigmatic histone variant in that it may form non-canonical nucleosomes. Three independent studies (mostly based on in vivo experiments) have shown that yeast CenH3 (Cse4) forms a centromere-specific nucleosome together with H4 and the non-histone protein Scm3 [19] [20] [21]. In fact, it has been suggested that Scm3 may be a Cse4-specific histone chaperone [21].…”

“…Three independent studies (mostly based on in vivo experiments) have shown that yeast CenH3 (Cse4) forms a centromere-specific nucleosome together with H4 and the non-histone protein Scm3 [19] [20] [21]. In fact, it has been suggested that Scm3 may be a Cse4-specific histone chaperone [21]. There is also evidence (mainly from in vivo protein -protein crosslinking) that cenH3 containing nucleosomes in Drosophila cell lines can exist as 'hemisomes', that is, that they consist of only one copy each of cenH3, H4, H2A, and H2B [22].…”

“…HIRA and CAF1 are specifically required to mediate H3 replacement with H3.3 [55]. Human RbAp46/48 assemble CenH3 into chromatin in vitro [57], however, Scm3 may also be involved [21]. Finally, Chz1 shows a preference for H2AZ-H2B over H2A-H2B and cooperates with the SWR1 complex in the exchange of H2A for H2A.Z [40] [58].…”

Structure of a CENP-A–histone H4 heterodimer in complex with chaperone HJURP

“…It is distantly related to the yeast centromeric protein Scm3 (Camahort et al 2007;Mizuguchi et al 2007;Stoler et al 2007;Sanchez-Pulido et al 2009). HJURP interacts directly with CENP-A and histone H4, localizes CENP-A to the centromere in a cell cycle-dependent manner, and enables the deposition of newly synthesized CENP-A into the centromeric nucleosome.…”

The Centromere: Epigenetic Control of Chromosome Segregation during Mitosis

“…CENP-A, as a specialized histone, has a specialized chaperone known as HJURP in humans or Scm3 in yeast. S. cerevisae Scm3 was identified in immunopurifications of CENP-A Cse4 and is required to target CENP-A Cse4 to centromeres (Camahort et al 2007;Mizuguchi et al 2007;Stoler et al 2007). Scm3 can assemble CENP-A Cse4 into nucleosomes in vitro (Shivaraju et al 2011).…”