Nascent peptide-dependent translation arrest is crucial for the quality control of eukaryotic gene expression. Here we show that the receptor for activated C kinase 1 (RACK1) participates in nascent peptide-dependent translation arrest, and that its binding to the 40S subunit is crucial for this. Translation arrest by a nascent peptide results in Dom34/Hbs1-independent endonucleolytic cleavage of mRNA, and this is stimulated by RACK1. We propose that RACK1 stimulates the translation arrest that is induced by basic amino-acid sequences that leads to endonucleolytic cleavage of the mRNA, as well as to co-translational protein degradation.

MAP kinases are integral to the mechanisms by which cells respond to a wide variety of environmental stresses. In Caenorhabditis elegans, the KGB-1 JNK signaling pathway regulates the response to heavy metal stress. In this study, we identified FOS-1, a bZIP transcription factor, as a target of KGB-1-mediated phosphorylation. We further identified two transcriptional targets of the KGB-1 pathway, kreg-1 and kreg-2/lys-3, which are required for the defense against heavy metal stress. FOS-1 plays a critical role in the transcriptional repression of the kreg-1 gene by recruiting histone deacetylase (HDAC) to its promoter. KGB-1 phosphorylation prevents FOS-1 dimerization and promoter binding, resulting in promoter derepression. Thus, HDAC behaves as a co-repressor modulating FOS-1-mediated transcriptional regulation. This study describes the direct link from JNK signaling, Fos phosphorylation, and regulation of kreg gene transcription, which modulates the stress response in C. elegans.