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The regular functioning of the nucleolus and nucleus-mitochondria crosstalk are considered unrelated processes, yet cytochrome c (Cc) migrates to the nucleus and even the nucleolus under stress conditions. Nucleolar liquid–liquid phase separation usually serves the cell as a fast, smart mechanism to control the spatial localization and trafcking of nuclear proteins. Actually, the alternative reading frame (ARF), a tumor suppressor protein sequestered by nucleophosmin (NPM) in the nucleoli, is shifted out from NPM upon DNA damage. DNA damage also triggers early translocation of respiratory Cc to nucleus before cytoplasmic caspase activation. Here, we show that Cc can bind to nucleolar NPM by triggering an extended-to-compact conformational change, driving ARF release. Such a NPM–Cc nucleolar interaction can be extended to a general mechanism for DNA damage in which the lysine-rich regions of Cc—rather than the canonical, arginine-rich stretches of membrane-less organelle components—controls the trafcking and availability of nucleolar proteins.

Stress granules are non-membrane bound RNA-protein granules essential for survival during acute cellular stress. TIA-1 is a key protein in the formation of stress granules that undergoes liquid-liquid phase separation by association with specific RNAs and protein-protein interactions. However, the fundamental properties of the TIA-1 protein that enable phase-separation also render TIA-1 susceptible to the formation of irreversible fibrillar aggregates. Despite this, within physiological stress granules, TIA-1 is not present as fibrils, pointing to additional factors within the cell that prevent TIA-1 aggregation. Here we show that heterotypic interactions with stress granule co-factors Zn2+ and RGG-rich regions from FUS each act together with nucleic acid to induce the liquid-liquid phase separation of TIA-1. In contrast, these co-factors do not enhance nucleic acid induced fibril formation of TIA-1, but rather robustly inhibit the process. NMR titration experiments revealed specific interactions between Zn2+ and H94 and H96 in RRM2 of TIA-1. Strikingly, this interaction promotes multimerization of TIA-1 independently of the prion-like domain. Thus, through different molecular mechanisms, these stress granule co-factors promote TIA-1 liquid-liquid phase separation and suppress fibrillar aggregates, potentially contributing to the dynamic nature of stress granules and the cellular protection that they provide.

The regular functioning of the nucleolus and nucleus-mitochondria crosstalk are considered unrelated processes, yet cytochrome c (Cc) migrates to the nucleus and even the nucleolus under stress conditions. Nucleolar liquid-liquid phase separation usually serves the cell as a fast, smart mechanism to control the spatial localization and trafficking of nuclear proteins. Actually, the alternative reading frame (ARF), a tumor suppressor protein sequestered by nucleophosmin (NPM) in the nucleoli, is shifted out from NPM upon DNA damage. DNA damage also triggers early translocation of respiratory Cc to nucleus before cytoplasmic caspase activation. Here, we show that Cc can bind to nucleolar NPM by triggering an extended-to-compact conformational change, driving ARF release. Such a NPM-Cc nucleolar interaction can be extended to a general mechanism for DNA damage in which the lysine-rich regions of Cc-rather than the canonical, arginine-rich stretches of membrane-less organelle components-controls the trafficking and availability of nucleolar proteins.

Despite mitochondria being key for the control of cell homeostasis and fate, their role in DNA damage response is usually just regarded as an apoptotic trigger. However, growing evidence points to mitochondrial factors modulating nuclear functions. Remarkably, after DNA damage, cytochrome c (Cc) interacts in the cell nucleus with a variety of well-known histone chaperones, whose activity is competitively inhibited by the haem protein. As nuclear Cc inhibits the nucleosome assembly/disassembly activity of histone chaperones, it might indeed affect chromatin dynamics and histone deposition on DNA. Several histone chaperones actually interact with Cc Lys residues through their acidic regions, which are also involved in heterotypic interactions leading to liquid–liquid phase transitions responsible for the assembly of nuclear condensates, including heterochromatin. This relies on dynamic histone–DNA interactions that can be modulated by acetylation of specific histone Lys residues. Thus, Cc may have a major regulatory role in DNA repair by fine-tuning nucleosome assembly activity and likely nuclear condensate formation.

The maintenance of genome integrity is a critical process for cell life. To face DNA lesions, living beings have developed a complex network called DNA damage response (DDR), which encompasses an intricate phosphorylation signalling cascade, enabling a quick DNA damage repair. To control this signalling cascade and to avoid an illegitimate activation, this network is tightly regulated by protein phosphatases, such as Protein Phosphatase 2A (PP2A). Moreover, histone chaperones assist the DNA repair mechanisms altering chromatin dynamics through their nucleosome assembly activity. Recent studies have reported that the mitochondrial respiratory protein cytochrome c is promptly translocated into the cell nucleus upon DNA damage, where it interacts with several histone chaperones. Within this context, the role of nuclear cytochrome c has been partially disclosed. Here, we have delved into the functional consequences of the novel DNA damage-induced complex formed by cytochrome c with the histone chaperones ANP32A and ANP32B. Strikingly, the heme protein impairs the PP2A inhibitory effect exerted by the histone chaperones ANP32A, ANP32B and SET/TAF-I. Furthermore, biophysical and structural approaches have been used to characterize the cytochrome c complex with ANP32A and ANP32B and to unveil the molecular mechanism underlying the cytoplasmic accumulation of ANP32B upon its phosphorylation. In addition, we have extended our knowledge on the histone chaperone regulation in the DDR by studying the Arabidopsis thaliana complex between cytochrome c and NRP1, a SET/TAF-I analogous. Herein we propose a novel standpoint about DDR regulation, in which cytochrome c exerts a modulating role on such signalling cascade through its interaction with histone chaperones, both by tuning their nucleosome assembly and PP2A inhibitory activity.

The design and unique feature of the first fast-ion loss detector (FILD) for the Mega Amp Spherical Tokamak - Upgrade (MAST-U) is presented here. The MAST-U FILD head is mounted on an axially and angularly actuated mechanism that makes it possible to independently adapt the orientation [0°, 90°] and radial position [1.40 m, 1.60 m] of the FILD head, i.e., its collimator, thus maximizing the detector velocity-space coverage in a broad range of plasma scenarios with different q95. The 3D geometry of the detector has been optimized to detect fast-ion losses from the neutral beam injectors. Orbit simulations are used to calculate the strike map and predict the expected signals. The results show a velocity-space range of [4 cm, 13 cm] in gyroradius and [30°, 85°] in pitch angle, covering the entire neutral beam ion energy range. The optical system will provide direct sight of the scintillator and simultaneous detection with two cameras, giving high spatial and temporal resolution. The MAST-U FILD will shed light on the dominant fast-ion transport mechanisms in one of the world’s two largest spherical tokamaks through absolute measurements of fast-ion losses

Malaria is caused by Apicomplexa protozoans from the Plasmodium genus entering the bloodstream of humans and animals through the bite of the female mosquitoes. The annotation of the Plasmodium vivax genome revealed a putative RNA binding protein (apiRBP) that was predicted to be trafficked into the apicoplast, a plastid organelle unique to Apicomplexa protozoans. Although a 3D structural model of the apiRBP corresponds to a noncanonical RNA recognition motif with an additional C-terminal ¿-helix (¿3), preliminary protein production trials were nevertheless unsuccessful. Theoretical solvation analysis of the apiRBP model highlighted an exposed hydrophobic region clustering ¿3. Hence, we used a C-terminal GFP-fused chimera to stabilize the highly insoluble apiRBP and determined its ability to bind U-rich stretches of RNA. The affinity of apiRBP toward such RNAs is highly dependent on ionic strength, suggesting that the apiRBP-RNA complex is driven by electrostatic interactions. Altogether, apiRBP represents an attractive tool for apicoplast transcriptional studies and for antimalarial drug design.

mRNA metabolism is tightly orchestrated by highly-regulated RNA Binding Proteins (RBPs) that determine mRNA fate, thereby influencing multiple cellular functions across biological contexts. Here, we review the interplay between six well-known RBPs (TTP, AUF-1, KSRP, HuR, TIA-1, and TIAR) that recognize AU-rich elements (AREs) at the 3′ untranslated regions of mRNAs, namely ARE-RBPs. Examples of the links between their cross-regulations and modulation of their targets are analyzed during mRNA processing, turnover, localization, and translational control. Furthermore, ARE recognition can be self-regulated by several factors that lead to the prevalence of one RBP over another. Consequently, we examine the factors that modulate the dynamics of those protein-RNA transient interactions to better understand the final consequences of the regulation mediated by ARE-RBPs. For instance, factors controlling the RBP isoforms, their conformational state or their post-translational modifications (PTMs) can strongly determine the fate of the protein-RNA complexes. Moreover, mRNA specific sequence and secondary structure or subtle environmental changes are also key determinants to take into account. To sum up, the whole understanding of such a fine tuned regulation is a challenge for future research and requires the integration of all the available structural and functional data by in vivo, in vitro and in silico approaches.

Higher-order plants and mammals use similar mechanisms to repair and tolerate oxidative DNA damage. Most studies on the DNA repair process have focused on yeast and mammals, in which histone chaperone-mediated nucleosome disassembly/reassembly is essential for DNA to be accessible to repair machinery. However, little is known about the specific role and modulation of histone chaperones in the context of DNA damage in plants. Here, the histone chaperone NRP1, which is closely related to human SET/TAF-Iβ, was found to exhibit nucleosome assembly activity in vitro and to accumulate in the chromatin of Arabidopsis thaliana after DNA breaks. In addition, this work establishes that NRP1 binds to cytochrome c, thereby preventing the former from binding to histones. Since NRP1 interacts with cytochrome c at its earmuff domain, that is, its histone-binding domain, cytochrome c thus competes with core histones and hampers the activity of NRP1 as a histone chaperone. Altogether, the results obtained indicate that the underlying molecular mechanisms in nucleosome disassembly/reassembly are highly conserved throughout evolution, as inferred from the similar inhibition of plant NRP1 and human SET/TAF-Iβ by cytochrome c during DNA damage response.

mRNA metabolism is tightly orchestrated by highly-regulated RNA Binding Proteins (RBPs) that determine mRNA fate, thereby influencing multiple cellular functions across biological contexts. Here, we review the interplay between six well-known RBPs (TTP, AUF-1, KSRP, HuR, TIA-1, and TIAR) that recognize AU-rich elements (AREs) at the 3' untranslated regions of mRNAs, namely ARE-RBPs. Examples of the links between their cross-regulations and modulation of their targets are analyzed during mRNA processing, turnover, localization, and translational control. Furthermore, ARE recognition can be self-regulated by several factors that lead to the prevalence of one RBP over another. Consequently, we examine the factors that modulate the dynamics of those protein-RNA transient interactions to better understand the final consequences of the regulation mediated by ARE-RBPs. For instance, factors controlling the RBP isoforms, their conformational state or their post-translational modifications (PTMs) can strongly determine the fate of the protein-RNA complexes. Moreover, mRNA specific sequence and secondary structure or subtle environmental changes are also key determinants to take into account. To sum up, the whole understanding of such a fine tuned regulation is a challenge for future research and requires the integration of all the available structural and functional data by in vivo, in vitro and in silico approaches.

Higher-order plants and mammals use similar mechanisms to repair and tolerate oxidative DNA damage. Most studies on the DNA repair process have focused on yeast and mammals, in which histone chaperone-mediated nucleosome disassembly/reassembly is essential for DNA to be accessible to repair machinery. However, little is known about the specific role and modulation of histone chaperones in the context of DNA damage in plants. Here, the histone chaperone NRP1, which is closely related to human SET/TAF-I , was found to exhibit nucleosome assembly activity in vitro and to accumulate in the chromatin of Arabidopsis thaliana after DNA breaks. In addition, this work establishes that NRP1 binds to cytochrome c, thereby preventing the former from binding to histones. Since NRP1 interacts with cytochrome c at its earmuff domain, that is, its histone-binding domain, cytochrome c thus competes with core histones and hampers the activity of NRP1 as a histone chaperone. Altogether, the results obtained indicate that the underlying molecularmechanisms in nucleosome disassembly/reassembly are highly conserved throughout evolution, as inferred from the similar inhibition of plant NRP1 and human SET/TAF-I by cytochrome c during DNA damage response