טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLavi Bar Ziv
SubjectRegulation of translation by signaling cascades in yeast
cells
DepartmentDepartment of Biology
Supervisor Professor Arava Yoav
Full Thesis textFull thesis text - English Version


Abstract

Cells must respond to changes in environmental conditions in order to survive. This response is characterized by a proteome change, which is often mediated by signal transduction pathways and regulated at both transcriptional and post-transcriptional levels. One of the most important regulatory mechanisms at the post-transcriptional level is the control of protein synthesis. Global translational regulation by signaling pathways in response to environmental changes was established before, while the translation regulation of specific mRNAs by these pathways still remains largely unknown. We try here to reveal the existence and the mechanism of translational control in face of cell-wall stress, which remains, thus far, unexplored.

One of the main stresses for yeast is cell wall stress, mediated through the PKC pathway. We found that cells that were subjected to cell-wall stress showed minor inhibition in global translation, accompanied by a slight phosphorylation of eIF2α. Both the translational inhibition and the phosphorylation of eIF2α are rapid and transient. Genome-wide analysis of the transcriptional changes reveals negligible adjustment of transcripts that focus mainly on cells' preparation for growth on fresh YPD rather than facing cell-wall stress. Genome-wide analysis of changes in polysomes association however, shows a cell-wall remodeling response, which is expressed by up-regulation of vesicular-transport proteins synthesis and down-reregulation of various cell-wall proteins synthesis. BGL2 appeared to be highly repressed in translation and was selected to further explore the regulation mechanism of this group. Fusion of BGL2 3’UTR to genes that showed different translational behavior conferred its translational phenotype upon them. Fusion of a different 3'UTR, from TPM1, to the BGL2 gene converted it to be translationally induced. These results suggest that translational control upon cell-wall stress exists and it is gene specific and mediated through the 3'UTR. Deletion of BGL2 3'UTR did not change its translational behavior, implying additional translation regulation modes. Alteration of these results during inactivation of the PKC pathway suggests a possible link to the signaling pathway mediating the cell response to cell-wall stress. Pkc1Δ cells proved to be too sensitive for the specific stress conditions used. However, milder hypotonic shock resulted in inconsistent results. A temporal inhibition, using staurosporine, of this pathway is required, which will allow the use of same shock conditions as used earlier.

Overall, our study revealed mRNA specific, 3'UTR based, translation regulation in response to cell wall stress and propose a method to link this translational regulation to the PKC pathway.