title: Conserved Asf1-importin β physical interaction in growth and sexual development in the ciliate Tetrahymena thermophila.
abstract: How the eukaryotic cell specifies distinct chromatin domains is a central problem in molecular biology. The ciliate protozoan Tetrahymena thermophila features a separation of structurally and functionally distinct germ-line and somatic chromatin into two distinct nuclei, the micronucleus (MIC) and macronucleus (MAC) respectively. To address questions about how distinct chromatin states are assembled in the MAC and MIC, we have initiated studies to define protein-protein interactions for T. thermophila chromatin-related proteins. Affinity purification followed by mass spectrometry analysis of the conserved Asf1 histone chaperone in T. thermophila revealed that it forms a complex with an importin β, ImpB6. Furthermore, these proteins co-localized to both the MAC and MIC in growth and development. We suggest that newly synthesized histones H3 and H4 in T. thermophila are transported via Asf1-ImpB6 in an evolutionarily conserved pathway to both nuclei where they then enter nucleus-specific chromatin assembly pathways. These studies set the stage for further use of functional proteomics to elucidate details of the characterization and functional analysis of the unique chromatin domains in T. thermophila.
  
  
  CONCLUSIONS
  Asf1 is an evolutionarily conserved chaperone of H3 and H4 histones that functions in replication dependent and independent chromatin assembly. Although Asf1 has been well studied in humans and yeast (members of the Opisthokonta lineage of eukaryotes), questions remain concerning its mechanism of function. To obtain additional insight into the Asf1 function we have initiated a proteomic analysis in the ciliate protozoan T. thermophila, a member of the Alveolata lineage of eukaryotes. Our results suggest that an evolutionarily conserved function of Asf1 is mediating the nuclear transport of newly synthesized histones H3 and H4.
authors.affiliation: Department of Biology, York University, 4700 Keele St., Toronto M3J 1P3, Canada.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Garg
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Lambert
authors.forename: Abdel
authors.initials: A
authors.lastname: Karsou
authors.forename: Susanna
authors.initials: S
authors.lastname: Marquez
authors.forename: Syed
authors.initials: S
authors.lastname: Nabeel-Shah
authors.forename: Virginia
authors.initials: V
authors.lastname: Bertucci
authors.forename: Dashaini V
authors.initials: DV
authors.lastname: Retnasothie
authors.forename: Ernest
authors.initials: E
authors.lastname: Radovani
authors.forename: Tony
authors.initials: T
authors.lastname: Pawson
authors.forename: Anne-Claude
authors.initials: AC
authors.lastname: Gingras
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Pearlman
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Fillingham
mesh_terms: D048648:Macronucleus / Q000378:metabolism*; D048631:Micronucleus, Germline / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*; D016808:Tetrahymena thermophila / Q000378:metabolism*; D028961:beta Karyopherins / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D015800:Protozoan Proteins; D028961:beta Karyopherins
keywords: Asf1; Chromatin; Proteomics; Tetrahymena