Sum1, a Component of the Fission Yeast eIF3 Translation Initiation Complex, Is Rapidly Relocalized During Environmental Stress and Interacts with Components of the 26S Proteasome

Abstract

Eukaryotic translation initiation factor 3 (eIF3) is a multisubunit complex that plays a central role in translation initiation. We show that fission yeast Sum1, which is structurally related to known eIF3 subunits in other species, is essential for translation initiation, whereas its overexpression results in reduced global translation. Sum1 is associated with the 40S ribosome and interacts stably with Int6, an eIF3 component, in vivo, suggesting that Sum1 is a component of the eIF3 complex. Sum1 is cytoplasmic under normal growth conditions. Surprisingly, Sum1 is rapidly relocalized to cytoplasmic foci after osmotic and thermal stress. Int6 and p116, another putative eIF3 subunit, behave similarly, suggesting that eIF3 is a dynamic complex. These cytoplasmic foci, which additionally comprise eIF4E and RNA components, may function as translation centers during environmental stress. After heat shock, Sum1 additionally colocalizes stably with the 26S proteasome at the nuclear periphery. The relationship between Sum1 and the 26S proteasome was further investigated, and we find cytoplasmic Sum1 localization to be dependent on the 26S proteasome. Furthermore, Sum1 interacts with the Mts2 and Mts4 components of the 26S proteasome. These data indicate a functional link between components of the structurally related eIF3 translation initiation and 26S proteasome complexes.

Processing bodies require RNA for assembly and contain nontranslating mRNAs

“…To date, we have been unable to visualize stress granules in Saccharomyces cereviseae under a variety of conditions (data not shown), although they can be detected in Saccharomyces pombe (Dunand-Sauthier et al 2002). However, several observations in mammalian cells suggest that P-bodies and stress granules are distinct structures.…”

Robust heat shock induces eIF2α-phosphorylation-independent assembly of stress granules containing eIF3 and 40S ribosomal subunits in budding yeast,Saccharomyces cerevisiae

“…It has been proposed that the SGs serve as triage sites redirecting mRNA to either translation, storage or degradation . Interestingly, SG-like structures, containing eIF3, have been found in heat-shocked fission yeast Schizosacchomyces pombe (Dunand-Sauthier et al, 2002), but have not yet been reported in Saccharomyces cerevisiae.…”

Metazoan stress granule assembly is mediated by P-eIF2α-dependent and -independent mechanisms

“…Until recently, bona fide SGs fitting all the above criteria were mainly reported in mammalian cells. However, several new studies have demonstrated the formation of SGs or SG-like bodies in Caenorhabditis elegans (Jud et al 2008), Trypanosoma brucei (Kramer et al 2008), Schizosaccharomyces pombe (Dunand-Sauthier et al 2002), and Saccharomyces cerevisiae (Buchan et al 2008;Groušl et al 2009), although SGs have yet to be documented in some other common model organisms such as Xenopus laevis, Danio rerio, and Drosophila melanogaster. The apparent evolutionary conservation of SGs as a stress survival mechanism underscores their importance throughout eukaryota.…”