Poster number 37 submitted by Qian He
The N-Terminal Domain of Eukaryotic Translation Initiation Factor 4B promotes P body Levels in Yeast
Qian He (SUNY at Buffalo, Department of Biological Sciences, Buffalo, NY), Ansuman Sahoo, Xiaozhuo Liu and Sarah E. Walker (SUNY at Buffalo, Department of Biological Sciences, Buffalo, NY)
P bodies are membrane-less cytoplasmic mRNA-protein (mRNP) granules conserved throughout eukaryotes for storage and degradation of mRNA. However, the mechanisms that mediate sorting of mRNAs into P bodies and other granules are not well understood. Eukaryotic initiation factor eIF4B, which accelerates the rate and stability of translation initiation complex assembly on mRNAs, has been shown to reside in P bodies in response to certain stresses in Saccharomyces cerevisiae. The NTD and 7-repeats of eIF4B promote translation of structured mRNAs and bind to the small subunit of the ribosome. We recently showed that the NTD also promotes resistance to various stressors by reprogramming translation of mRNAs known to aggregate in P bodies. Here we investigated whether P bodies and resulting mRNA turnover play a role in translation reprogramming mediated by eIF4B. First, we determined that eIF4B enhanced resting P bodies levels in yeast, by following localization of Edc3-GFP, a protein localized to these cytoplasmic mRNP granules. Deletion of the NTD of eIF4B decreased the number of P bodies per cell, but deletion of the RRM, which promotes RNA binding, or the 7-repeats domain, which like the NTD stimulates mRNA recruitment to the ribosome, but with a more deleterious phenotype, did not affect P body levels. Consistent with a specific role for the eIF4B NTD in promoting P body levels, we found that an eIF4A mutant compromised in eIF4B interaction showed reduced P body formation when eIF4B ∆ntd was overexpressed. Current work is exploring additional interactions of eIF4B and their roles in P body formation and stability. Together these data suggest that eIF4B plays a direct role in assembly or maintenance of P bodies, and that changes in translatome composition as a result of this activity allows resistance of yeast to various stressors. This work also highlights the impact of mRNA structure in the granule-mediated degradation of mRNAs through competition with translation.
Keywords: eIF4B, P bodies, Translation initiation