title: A systematic genetic screen identifies new factors  influencing centromeric heterochromatin integrity  in fission yeast.
abstract: BACKGROUND
  Heterochromatin plays important roles in the regulation and stability of eukaryotic genomes. Both heterochromatin components and pathways that promote heterochromatin assembly, including RNA interference, RNAi, are broadly conserved between the fission yeast Schizosaccharomyces pombe and humans. As a result, fission yeast has emerged as an important model system for dissecting mechanisms governing heterochromatin integrity. Thus far, over 50 proteins have been found to contribute to heterochromatin assembly at fission yeast centromeres. However, previous studies have not been exhaustive, and it is therefore likely that further factors remain to be identified.
  
  
  RESULTS
  To gain a more complete understanding of heterochromatin assembly pathways, we have performed a systematic genetic screen for factors required for centromeric heterochromatin integrity. In addition to known RNAi and chromatin modification components, we identified several proteins with previously undescribed roles in heterochromatin regulation. These included both known and newly characterised splicing-associated proteins,which are required for proper processing of centromeric transcripts by the RNAi pathway, and COP9 signalosome components Csn1 and Csn2, whose role in heterochromatin assembly can be explained at least in part by a role in the Ddb1-dependent degradation of the heterochromatin regulator Epe1.
  
  
  CONCLUSIONS
  This work has revealed new factors involved in RNAi-directed heterochromatin assembly in fission yeast. Our findings support and extend previous observations that implicate components of the splicing machinery as a platform for RNAi, and demonstrate a novel role for the COP9 signalosome in heterochromatin regulation.
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, Edinburgh EH9 3JR, UK. elizabeth.bayne@ed.ac.uk
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Bayne
authors.forename: Dominika A
authors.initials: DA
authors.lastname: Bijos
authors.forename: Sharon A
authors.initials: SA
authors.lastname: White
authors.forename: Flavia
authors.initials: F
authors.lastname: de Lima Alves
authors.forename: Juri
authors.initials: J
authors.lastname: Rappsilber
authors.forename: Robin C
authors.initials: RC
authors.lastname: Allshire
mesh_terms: D002503:Centromere; D015966:Gene Expression Regulation, Fungal; D006570:Heterochromatin / Q000378:metabolism*; D034622:RNA Interference; D012568:Schizosaccharomyces / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D006570:Heterochromatin; D029702:Schizosaccharomyces pombe Proteins