Khawaja, S. | Search bioRxiv

bioRxiv2024

Polysomes and mRNA control the biophysical properties of the eukaryotic cytoplasm

The organization and biophysical properties of the cytoplasm influence all cellular reactions, including molecular interactions and the mobility of biomolecules. It has become clear that the cytoplasm does not behave like a simple fluid but instead is a densely crowded and highly organized environment. Yet, the detailed properties of the cytoplasm, the molecular mechanisms that control them and how they influence the biochemistry of cells remain poorly understood. Here, we investigate the diffusive properties of the cytoplasm in silico and in vivo, employing mRNPs (messenger ribonucleoprotein) and GEM (genetically encoded multimeric) particles as rheological probes in proliferating cells. We demonstrate that cytoplasmic diffusivity increases upon polysome disassembly due to translation inhibition or upon a reduction in mRNA levels. Reducing ribosome concentration by up to 20-25% without a change in polysome levels has no effect in vivo. In addition, we show that upon polysome disassembly, mRNA condensation into P-bodies does not affect cytosolic diffusion in budding yeast. Altogether, our results show that mRNAs and their organization into polysomes control the biophysical properties of the eukaryotic cytoplasm. HighlightsO_LIPolysomes control the biophysical properties of cytoplasm. C_LIO_LImRNP and GEM mobility is enhanced upon translation inhibition that leads to polysome disassembly C_LIO_LIPerturbation of mRNA levels leads to an increase in cytosolic diffusion. C_LI

cell biology↗

bioRxiv2024

Newly synthesized mRNA selectively escapes translational repression following acute stress.

When cells encounter environmental stress, they rapidly mount an adaptive response by switching from pro-growth to stress-responsive gene expression programs. It is poorly understood how cells selectively silence pre-existing, pro-growth transcripts, yet efficiently translate transcriptionally-induced stress mRNA, and whether these transcriptional and post-transcriptional responses are coordinated. Here, we show that following acute glucose withdrawal in S. cerevisiae, pre-existing mRNAs are not first degraded to halt protein synthesis, nor are they sequestered away in P-bodies. Rather, their translation is rapidly repressed through a sequence-independent mechanism that differentiates between mRNAs produced before and after stress followed by their decay. Transcriptional induction of endogenous transcripts and reporter mRNAs during stress is sufficient to escape translational repression, while induction prior to stress leads to repression. Our results reveal a timing-controlled coordination of the transcriptional and translational responses in the nucleus and cytoplasm ensuring a rapid and widescale reprogramming of gene expression following environmental stress.

molecular biology↗