Post-transcriptional regulation in the myo1Δ mutant of Saccharomyces cerevisiae

Background: Saccharomyces cerevisiae myosin type II-deficient (myo1 Delta) strains remain viable and divide, despite the absence of a cytokinetic ring, by activation of the PKC1 dependent cell wall integrity pathway (CWIP). Since the myo1 Delta transcriptional fingerprint is a subset of the CWIP fingerprint, the myo1 Delta strain may provide a simplified paradigm for cell wall stress survival. Results: To explore the post-transcriptional regulation of the myo1 Delta stress response, 1,301 differentially regulated ribosome-bound mRNAs were identified by microarray analysis of which 204 were co-regulated by transcription and translation. Four categories of mRNA were significantly affected - protein biosynthesis, metabolism, carbohydrate metabolism, and unknown functions. Nine genes of the 20 CWIP fingerprint genes were post-transcriptionally regulated. Down and up regulation of selected ribosomal protein and cell wall biosynthesis mRNAs was validated by their distribution in polysomes from wild type and myo1 Delta strains. Western blot analysis revealed accumulation of the phosphorylated form of eukaryotic translation initiation factor 2 (eIF2 alpha-P) and a reduction in the steady state levels of the translation initiation factor eIF4Gp in myo1 Delta strains. Deletion of GCN2 in myo1 Delta abolished eIF2 alpha p phosphorylation, and showed a severe growth defect. The presence of P-bodies in myo1 Delta strains suggests that the process of mRNA sequestration is active, however, the three representative down regulated RP mRNAs, RPS8A, RPL3 and RPL7B were present at equivalent levels in Dcp2p-mCh-positive immunoprecipitated fractions from myo1 Delta and wild type cells. These same RP mRNAs were also selectively co-precipitated with eIF2 alpha-P in myo1 Delta strains. Conclusions: Quantitative analysis of ribosome-associated mRNAs and their polyribosome distributions suggests selective regulation of mRNA translation efficiency in myo1 Delta strains. Inhibition of translation initiation factor eIF2 alpha (eIF2 alpha-P) in these strains was by Gcn2p-dependent phosphorylation. The increase in the levels of eIF2 alpha-P; the genetic interaction between GCN2 and MYO1; and the reduced levels of eIF4Gp suggest that other signaling pathways, in addition to the CWIP, may be important for myo1 Delta strain survival. Selective co-immunoprecipitation of RP mRNAs with eIF2 alpha-P in myo1 Delta strains suggests a novel mode of translational regulation. These results indicate that post-transcriptional control is important in the myo1 Delta stress response and possibly other stresses in yeast.