Mol. Biol. Cell, in press

Rck2 is required for reprogramming of ribosomes during oxidative stress

Swaminathan S, Masek T, Molin C, Pospisek M, Sunnerhagen P

Lundberg Laboratory, Department of Cell and Molecular Biology, Göteborg University, P.O. Box 462, 405 30, Göteborg, Sweden.

Rck2 is a MAP kinase-regulated protein kinase in yeast implicated in translational regulation. rck2D mutants are mildly sensitive to oxidative stress, a condition which causes dissociation of actively translating ribosomes (polysomes). In rck2D cells, polysomes are lost to an even higher degree than the wild-type upon stress. Cells overexpressing the catalytically inactive rck2-kd allele are highly sensitive to oxidative stress. In such cells, dissociation of polysomes upon stress was instead greatly delayed. The protein synthesis rate decreased to a similar degree as in wild-type cells, however, indicating that in rck2-kd cells, the polysome complexes were inactive. Array analyses of total and polysome-associated mRNAs revealed major deregulation of the translational machinery in rck2 mutant cells. This involves transcripts for cytosolic ribosomal proteins and for processing and assembly of ribosomes. In rck2D cells, weakly transcribed mRNAs associate more avidly with polysomes than in wild-type cells, while the opposite holds true for rck2-kd cells. This is consistent with perturbed regulation of translation elongation, which is predicted to alter the ratio between mRNAs with and without strong entry sites at ribosomes. We infer that imbalances in the translational apparatus are a major reason for the inability of these cells to respond to stress.