title: In vivo evidence that eIF3 stays bound to ribosomes elongating and terminating on short upstream ORFs to promote reinitiation.
abstract: Translation reinitiation is a gene-specific translational control mechanism characterized by the ability of some short upstream ORFs to prevent recycling of the post-termination 40S subunit in order to resume scanning for reinitiation downstream. Its efficiency decreases with the increasing uORF length, or by the presence of secondary structures, suggesting that the time taken to translate a uORF is more critical than its length. This led to a hypothesis that some initiation factors needed for reinitiation are preserved on the 80S ribosome during early elongation. Here, using the GCN4 mRNA containing four short uORFs, we developed a novel in vivo RNA-protein Ni2+-pull down assay to demonstrate for the first time that one of these initiation factors is eIF3. eIF3 but not eIF2 preferentially associates with RNA segments encompassing two GCN4 reinitiation-permissive uORFs, uORF1 and uORF2, containing cis-acting 5΄ reinitiation-promoting elements (RPEs). We show that the preferred association of eIF3 with these uORFs is dependent on intact RPEs and the eIF3a/TIF32 subunit and sharply declines with the extended length of uORFs. Our data thus imply that eIF3 travels with early elongating ribosomes and that the RPEs interact with eIF3 in order to stabilize the mRNA-eIF3-40S post-termination complex to stimulate efficient reinitiation downstream.
authors.affiliation: Laboratory of Regulation of Gene Expression, Institute of Microbiology AS CR, Prague, Videnska 1083, 142 20, Czech Republic.
authors.forename: Mahabub Pasha
authors.initials: MP
authors.lastname: Mohammad
authors.affiliation: Laboratory of Regulation of Gene Expression, Institute of Microbiology AS CR, Prague, Videnska 1083, 142 20, Czech Republic.
authors.forename: Vanda
authors.initials: V
authors.lastname: Munzarová Pondelícková
authors.affiliation: Laboratory of Regulation of Gene Expression, Institute of Microbiology AS CR, Prague, Videnska 1083, 142 20, Czech Republic.
authors.forename: Jakub
authors.initials: J
authors.lastname: Zeman
authors.affiliation: Laboratory of Regulation of Gene Expression, Institute of Microbiology AS CR, Prague, Videnska 1083, 142 20, Czech Republic.
authors.forename: Stanislava
authors.initials: S
authors.lastname: Gunišová
authors.affiliation: Laboratory of Regulation of Gene Expression, Institute of Microbiology AS CR, Prague, Videnska 1083, 142 20, Czech Republic.
authors.forename: Leoš Shivaya
authors.initials: LS
authors.lastname: Valášek
mesh_terms: D020121:5' Untranslated Regions; D018388:Codon, Terminator; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism*; D005786:Gene Expression Regulation; D005821:Genetic Techniques; D016366:Open Reading Frames; D010441:Peptide Chain Elongation, Translational; D010442:Peptide Chain Initiation, Translational; D010443:Peptide Chain Termination, Translational; D054682:Ribosome Subunits, Small, Eukaryotic / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D018388:Codon, Terminator; D039621:Eukaryotic Initiation Factor-3