Targeted mRNA cleavage by a stress‐activated, p38‐ATF/CREB pathway

Mitogen/stress‐activated protein kinases (MAPK/SAPK) of the p38 family regulate multiple cellular processes that include survival, differentiation, and death. They transduce signals via bZIP transcription factors of the ATF/CREB family, such as ATF2 and Jun, to regulate the transcription of target genes. Upon stress, the fission yeast Spc1 kinase‐regulated, Atf1‐Pcr1 heterodimer triggers the cleavage of mRNAs that contain an M26 ( CRE ‐like) site within the transcribed region. Transcription shut‐off and modified RLM‐RACE experiments revealed that cleavage is post‐transcriptional. Engineered M26 sites at different locations in the ORF each triggered mRNA cleavage in their vicinity, demonstrating that the position of the M26 site dictates where the transcript is cleaved. Such cleavage renders the mRNAs unsuitable for translation. This stress‐activated gene silencing (SGS) leads to reduce the expression of target genes without shutting off transcription itself. Thus, a single p38‐ATF/CREB pathway can coordinately induce (promote transcription) and repress (SGS) distinct subsets of genes, as is required for developmental decisions in response to stress and other stimuli. We have identified RNA enzymes that co‐purify with Atf1‐Pcr1. We developed a positive selection approach to identify components of the SGS pathway. These pave the way for systemic and comprehensive dissection of pathway mechanisms.