is-tagged GCN5 protein and 0.05 mCi of acetyl-CoA, as described previously. Transfection of siRNA oligonucleotides The sequences designed to specifically target human SRSF2, Tip60, HDAC6, srpk1 and srpk2 RNAs are listed in the Supplementary data. Cells were transfected with siRNA oligonucleotides duplex using Oligofectamine reagent according to the manufacturer’s instructions, excepted for H810 cells transfected with Hi-Perfect reagent. The cells were analysed 72 h after transfection. Quantitative RTPCR and RTPCR analyses Quantitative RTPCR was performed on Stratagene MX3005P apparatus, as previously described. The specific primers used for mRNA amplification are described in the Supplementary data. RTPCR Acetylation PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19827996 controls SRSF2 protein level V Edmond et al analysis of caspase-8 splice variants was performed as described previously. Supplementary data Supplementary data are available at The EMBO Journal Online. Nationale contre le Cancer and by ‘the Conseil Scientifique National d’AGIR a dom. This work was ‘supported by the Comite Departemental Isere de la Ligue Nationale contre le Cancer. Valerie Edmond was supported by a grant from the ‘Conseil Scientifique National d’AGIR a dom. SK laboratory is supported by ANR, ARC, INCa. Acknowledgements We thank Patricia Betton, Pascal Perron and IMR-1 price Celine Barrial-Lampreia for technical assistance. This work was supported by the Ligue Conflict of interest The authors declare that they have no conflict of interest. Eukaryotic chromosomes consist of repeating structural units known as nucleosomes. The structure of the nucleosome is comprised of a canonical histone octamer containing two histone H2A-H2B dimers and a histone 2 tetramer, which together are surrounded by B146 base pairs of DNA. CenH3 and H2A.Z are evolutionarily conserved histone variants with specific cellular localization patterns. Centromere-specific nucleosomes containing CenH3 serve as the sites for kinetochore assembly. Nucleosomes containing H2A.Z are enriched in the promoter regions of most genes as well as in the pericentromeric regions of chromosomes, suggesting that H2A.Z contributes to chromosome segregation. There is much debate over the composition of centromerespecific nucleosomes. A recent report indicated that the centromere-specific octameric nucleosomes are composed of Cse4 and histones H2A, H2B, and H4. Other studies showed that centromere-specific nucleosomes contain Cse4, histone H4, and the non-histone protein Scm3, but not histone H2A or H2B. However, it is unclear whether Scm3 is a component of centromere-specific nucleosomes. Controversy also exists over the three-dimensional structure of centromerespecific nucleosomes. A recent report showed that CenH3containing nucleosomes were suggested to induce positive DNA supercoils and wrap DNA in a right-handed manner, in contrast to canonical nucleosomes, which wrap DNA in a lefthanded manner, with negative supercoiling. However, a recent study of the structure of 2 showed no evidence for positive DNA supercoils. Therefore, a variety of further experimental approaches are needed to establish the threedimensional state of the centromere-specific nucleosomes. In addition to the Cse4-containing centromere-specific nucleosomes, several studies have explored the roles of the canonical histones in chromosome segregation. The temperature sensitivity of a histone H4 double substitution mutant defective in mitotic chromosome transmission was reversed by Cse4 overexpression in