An mRNA decapping mutant deficient in P body assembly limits mRNA stabilization in response to osmotic stress

Yeast is exposed to changing environmental conditions and must adapt its genetic program to provide a homeostatic intracellular environment. An important stress for yeast in the wild is high osmolarity. A key response to this stress is increased mRNA stability primarily by the inhibition of deadenylation. We previously demonstrated that mutations in decapping activators (edc3 Delta lsm4 Delta C), which result in defects in P body assembly, can destabilize mRNA under unstressed conditions. We wished to examine whether mRNA would be destabilized in the edc3 Delta lsm4 Delta C mutant as compared to the wild-type in response to osmotic stress, when P bodies are intense and numerous. Our results show that the edc3 Delta lsm4 Delta C mutant limits the mRNA stability in response to osmotic stress, while the magnitude of stabilization was similar as compared to the wild-type. The reduced mRNA stability in the edc3 Delta lsm4 Delta C mutant was correlated with a shorter PGK1 poly(A) tail. Similarly, the MFA2 mRNA was more rapidly deadenylated as well as significantly stabilized in the ccr4 Delta deadenylation mutant in the edc3 Delta lsm4 Delta C background. These results suggest a role for these decapping factors in stabilizing mRNA and may implicate P bodies as sites of reduced mRNA degradation.