title: Histone chaperone Asf1 plays an essential role in maintaining genomic stability in fission yeast.
abstract: The histone H3-H4 chaperone Asf1 is involved in chromatin assembly (or disassembly), histone exchange, regulation of transcription, and chromatin silencing in several organisms. To investigate the essential functions of Asf1 in Schizosaccharomyces pombe, asf1-ts mutants were constructed by random mutagenesis using PCR. One mutant (asf1-33(ts)) was mated with mutants in 77 different kinase genes to identify synthetic lethal combinations. The asf1-33 mutant required the DNA damage checkpoint factors Chk1 and Rad3 for its survival at the restrictive temperature. Chk1, but not Cds1, was phosphorylated in the asf1-33 mutant at the restrictive temperature, indicating that the DNA damage checkpoint was activated in the asf1-33 mutant. DNA damage occured in the asf1-33 mutant, with degradation of the chromosomal DNA observed through pulse-field gel electrophoresis and the formation of Rad22 foci. Sensitivity to micrococcal nuclease in the asf1-33 mutant was increased compared to the asf1(+) strain at the restrictive temperature, suggesting that asf1 mutations also caused a defect in overall chromatin structure. The Asf1-33 mutant protein was mislocalized and incapable of binding histones. Furthermore, histone H3 levels at the centromeric outer repeat region were decreased in the asf1-33 mutant and heterochromatin structure was impaired. Finally, sim3, which encodes a CenH3 histone chaperone, was identified as a strong suppressor of the asf1-33 mutant. Taken together, these results clearly indicate that Asf1 plays an essential role in maintaining genomic stability in S. pombe.
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Tanae
authors.forename: Tomitaka
authors.initials: T
authors.lastname: Horiuchi
authors.forename: Yuzy
authors.initials: Y
authors.lastname: Matsuo
authors.forename: Satoshi
authors.initials: S
authors.lastname: Katayama
authors.forename: Makoto
authors.initials: M
authors.lastname: Kawamukai
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D059447:Cell Cycle Checkpoints / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000502:physiology; D048430:Cell Shape / Q000235:genetics; D002470:Cell Survival / Q000235:genetics; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D042822:Genomic Instability / Q000235:genetics*; D056488:Histone Chaperones / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D006657:Histones / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D030781:Organisms, Genetically Modified; D011485:Protein Binding / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics* / Q000502:physiology; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013696:Temperature
chemical_list: D018797:Cell Cycle Proteins; C524040:Cia1 protein, S pombe; D056488:Histone Chaperones; D006657:Histones; D018832:Molecular Chaperones; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; D000071877:Checkpoint Kinase 1; C000605873:Chk1 protein, S pombe; C456840:rad3 protein, S pombe