title: PCI proteins eIF3e and eIF3m define distinct translation initiation factor 3 complexes.
abstract: BACKGROUND
  PCI/MPN domain protein complexes comprise the 19S proteasome lid, the COP9 signalosome (CSN), and eukaryotic translation initiation factor 3 (eIF3). The eIF3 complex is thought to be composed of essential core subunits required for global protein synthesis and non-essential subunits that may modulate mRNA specificity. Interactions of unclear significance were reported between eIF3 subunits and PCI proteins contained in the CSN.
  
  
  RESULTS
  Here, we report the unexpected finding that fission yeast has two distinct eIF3 complexes sharing common core subunits, but distinguished by the PCI proteins eIF3e and the novel eIF3m, which was previously annotated as a putative CSN subunit. Whereas neither eIF3e nor eIF3m contribute to the non-essential activities of CSN in cullin-RING ubiquitin ligase control, eif3m, unlike eif3e, is an essential gene required for global cellular protein synthesis and polysome formation. Using a ribonomic approach, this phenotypic distinction was correlated with a different set of mRNAs associated with the eIF3e and eIF3m complexes. Whereas the eIF3m complex appears to associate with the bulk of cellular mRNAs, the eIF3e complex associates with a far more restricted set. The microarray findings were independently corroborated for a random set of 14 mRNAs by RT-PCR analysis.
  
  
  CONCLUSIONS
  We propose that the PCI proteins eIF3e and eIF3m define distinct eIF3 complexes that may assist in the translation of different sets of mRNAs.
authors.affiliation: Department of Genetics and Complex Diseases, Harvard School of Public Health, 665 Huntington Avenue, Boston, Massachusetts 02115, USA. czhou@rics.bwh.harvard.edu
authors.forename: Chunshui
authors.initials: C
authors.lastname: Zhou
authors.forename: Fatih
authors.initials: F
authors.lastname: Arslan
authors.forename: Susan
authors.initials: S
authors.lastname: Wee
authors.forename: Srinivasan
authors.initials: S
authors.lastname: Krishnan
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Ivanov
authors.forename: Anna
authors.initials: A
authors.lastname: Oliva
authors.forename: Janet
authors.initials: J
authors.lastname: Leatherwood
authors.forename: Dieter A
authors.initials: DA
authors.lastname: Wolf
mesh_terms: D039621:Eukaryotic Initiation Factor-3 / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex / Q000096:biosynthesis* / Q000235:genetics*; D014176:Protein Biosynthesis / Q000235:genetics*; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism
chemical_list: D039621:Eukaryotic Initiation Factor-3; D046988:Proteasome Endopeptidase Complex