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Whitman BT, Wang Y, Murray CRA, Glover MJN, Owttrim GW. Liquid-Liquid Phase Separation of the DEAD-Box Cyanobacterial RNA Helicase Redox (CrhR) into Dynamic Membraneless Organelles in Synechocystis sp. Strain PCC 6803. Appl Environ Microbiol 2023; 89:e0001523. [PMID: 36920190 PMCID: PMC10132119 DOI: 10.1128/aem.00015-23] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 02/17/2023] [Indexed: 03/16/2023] Open
Abstract
Compartmentalization of macromolecules into discrete non-lipid-bound bodies by liquid-liquid phase separation (LLPS) is a well-characterized regulatory mechanism frequently associated with the cellular stress response in eukaryotes. In contrast, the formation and importance of similar complexes is just becoming evident in bacteria. Here, we identify LLPS as the mechanism by which the DEAD-box RNA helicase, cyanobacterial RNA helicase redox (CrhR), compartmentalizes into dynamic membraneless organelles in a temporal and spatial manner in response to abiotic stress in the cyanobacterium Synechocystis sp. strain PCC 6803. Stress conditions induced CrhR to form a single crescent localized exterior to the thylakoid membrane, indicating that this region is a crucial domain in the cyanobacterial stress response. These crescents rapidly dissipate upon alleviation of the stress conditions. Furthermore, CrhR aggregation was mediated by LLPS in an RNA-dependent reaction. We propose that dynamic CrhR condensation performs crucial roles in RNA metabolism, enabling rapid adaptation of the photosynthetic apparatus to environmental stresses. These results expand our understanding of the role that functional compartmentalization of RNA helicases and thus RNA processing in membraneless organelles by LLPS-mediated protein condensation performs in the bacterial response to environmental stress. IMPORTANCE Oxygen-evolving photosynthetic cyanobacteria evolved ~3 billion years ago, performing fundamental roles in the biogeochemical evolution of the early Earth and continue to perform fundamental roles in nutrient cycling and primary productivity today. The phylum consists of diverse species that flourish in heterogeneous environments. A prime driver for survival is the ability to alter photosynthetic performance in response to the shifting environmental conditions these organisms continuously encounter. This study demonstrated that diverse abiotic stresses elicit dramatic changes in localization and structural organization of the RNA helicase CrhR associated with the photosynthetic thylakoid membrane. These dynamic changes, mediated by a liquid-liquid phase separation (LLPS)-mediated mechanism, reveal a novel mechanism by which cyanobacteria can compartmentalize the activity of ribonucleoprotein complexes in membraneless organelles. The results have significant consequences for understanding bacterial adaptation and survival in response to changing environmental conditions.
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Affiliation(s)
- Brendan T. Whitman
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Yixiong Wang
- Department of Oncology, Cross Cancer Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Cameron R. A. Murray
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Mark J. N. Glover
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - George W. Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
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2
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Ritter SPA, Brand LA, Vincent SL, Rosana ARR, Lewis AC, Whitford DS, Owttrim GW. Multiple Light-Dark Signals Regulate Expression of the DEAD-Box RNA Helicase CrhR in Synechocystis PCC 6803. Cells 2022; 11:3397. [PMID: 36359793 PMCID: PMC9655292 DOI: 10.3390/cells11213397] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 10/18/2022] [Accepted: 10/20/2022] [Indexed: 09/08/2024] Open
Abstract
Since oxygenic photosynthesis evolved in the common ancestor of cyanobacteria during the Archean, a range of sensing and response strategies evolved to allow efficient acclimation to the fluctuating light conditions experienced in the diverse environments they inhabit. However, how these regulatory mechanisms are assimilated at the molecular level to coordinate individual gene expression is still being elucidated. Here, we demonstrate that integration of a series of three distinct light signals generate an unexpectedly complex network regulating expression of the sole DEAD-box RNA helicase, CrhR, encoded in Synechocystis sp. PCC 6803. The mechanisms function at the transcriptional, translational and post-translation levels, fine-tuning CrhR abundance to permit rapid acclimation to fluctuating light and temperature regimes. CrhR abundance is enhanced 15-fold by low temperature stress. We initially confirmed that the primary mechanism controlling crhR transcript accumulation at 20 °C requires a light quantity-driven reduction of the redox poise in the vicinity of the plastoquinone pool. Once transcribed, a specific light quality cue, a red light signal, was required for crhR translation, far-red reversal of which indicates a phytochrome-mediated mechanism. Examination of CrhR repression at 30 °C revealed that a redox- and light quality-independent light signal was required to initiate CrhR degradation. The crucial role of light was further revealed by the observation that dark conditions superseded the light signals required to initiate each of these regulatory processes. The findings reveal an unexpected complexity of light-dark sensing and signaling that regulate expression of an individual gene in cyanobacteria, an integrated mechanism of environmental perception not previously reported.
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Affiliation(s)
- Sean P. A. Ritter
- Department of Botany, University of British Columbia, 3156-6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
| | - Logan A. Brand
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Shelby L. Vincent
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | | | - Allison C. Lewis
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstraße 108, 01307 Dresden, Germany
| | - Denise S. Whitford
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - George W. Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
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3
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Whitman BT, Murray CRA, Whitford DS, Paul SS, Fahlman RP, Glover MJN, Owttrim GW. Degron-mediated proteolysis of CrhR-like DEAD-box RNA helicases in cyanobacteria. J Biol Chem 2022; 298:101925. [PMID: 35413287 PMCID: PMC9117542 DOI: 10.1016/j.jbc.2022.101925] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 04/01/2022] [Accepted: 04/02/2022] [Indexed: 11/18/2022] Open
Abstract
Conditional proteolytic degradation is an irreversible and highly regulated process that fulfills crucial regulatory functions in all organisms. As proteolytic targets tend to be critical metabolic or regulatory proteins, substrates are targeted for degradation only under appropriate conditions through the recognition of an amino acid sequence referred to as a “degron”. DEAD-box RNA helicases mediate all aspects of RNA metabolism, contributing to cellular fitness. However, the mechanism by which abiotic-stress modulation of protein stability regulates bacterial helicase abundance has not been extensively characterized. Here, we provide in vivo evidence that proteolytic degradation of the cyanobacterial DEAD-box RNA helicase CrhR is conditional, being initiated by a temperature upshift from 20 to 30 °C in the model cyanobacterium, Synechocystis sp. PCC 6803. We show degradation requires a unique, highly conserved, inherently bipartite degron located in the C-terminal extension found only in CrhR-related RNA helicases in the phylum Cyanobacteria. However, although necessary, the degron is not sufficient for proteolysis, as disruption of RNA helicase activity and/or translation inhibits degradation. These results suggest a positive feedback mechanism involving a role for CrhR in expression of a crucial factor required for degradation. Furthermore, AlphaFold structural prediction indicated the C-terminal extension is a homodimerization domain with homology to other bacterial RNA helicases, and mass photometry data confirmed that CrhR exists as a dimer in solution at 22 °C. These structural data suggest a model wherein the CrhR degron is occluded at the dimerization interface but could be exposed if dimerization was disrupted by nonpermissive conditions.
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Affiliation(s)
- Brendan T Whitman
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Cameron R A Murray
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Denise S Whitford
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - Simanta S Paul
- Department of Physics, University of Alberta, Edmonton, Alberta, Canada
| | - Richard P Fahlman
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Mark J N Glover
- Department of Biochemistry, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - George W Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
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4
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Rosana ARR, Whitford DS, Migur A, Steglich C, Kujat-Choy SL, Hess WR, Owttrim GW. RNA helicase-regulated processing of the Synechocystis rimO-crhR operon results in differential cistron expression and accumulation of two sRNAs. J Biol Chem 2020; 295:6372-6386. [PMID: 32209657 DOI: 10.1074/jbc.ra120.013148] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 03/19/2020] [Indexed: 12/21/2022] Open
Abstract
The arrangement of functionally-related genes in operons is a fundamental element of how genetic information is organized in prokaryotes. This organization ensures coordinated gene expression by co-transcription. Often, however, alternative genetic responses to specific stress conditions demand the discoordination of operon expression. During cold temperature stress, accumulation of the gene encoding the sole Asp-Glu-Ala-Asp (DEAD)-box RNA helicase in Synechocystis sp. PCC 6803, crhR (slr0083), increases 15-fold. Here, we show that crhR is expressed from a dicistronic operon with the methylthiotransferase rimO/miaB (slr0082) gene, followed by rapid processing of the operon transcript into two monocistronic mRNAs. This cleavage event is required for and results in destabilization of the rimO transcript. Results from secondary structure modeling and analysis of RNase E cleavage of the rimO-crhR transcript in vitro suggested that CrhR plays a role in enhancing the rate of the processing in an auto-regulatory manner. Moreover, two putative small RNAs are generated from additional processing, degradation, or both of the rimO transcript. These results suggest a role for the bacterial RNA helicase CrhR in RNase E-dependent mRNA processing in Synechocystis and expand the known range of organisms possessing small RNAs derived from processing of mRNA transcripts.
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Affiliation(s)
- Albert Remus R Rosana
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Denise S Whitford
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Anzhela Migur
- Faculty of Biology, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany
| | - Claudia Steglich
- Faculty of Biology, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany
| | - Sonya L Kujat-Choy
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Wolfgang R Hess
- Faculty of Biology, University of Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.,Freiburg Institute for Advanced Studies, University of Freiburg, Albertstrasse 19, D-79104 Freiburg, Germany
| | - George W Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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5
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Kamjula V, Kanneganti A, Metla R, Nidamanuri K, Idupulapati S, Runthala A. Decoding the vital segments in human ATP-dependent RNA helicase. Bioinformation 2020; 16:160-170. [PMID: 32405168 PMCID: PMC7196165 DOI: 10.6026/97320630016160] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 02/20/2020] [Indexed: 12/28/2022] Open
Abstract
An analysis of the ATP-dependent RNA helicase using known functionally close analogs helps disclose the structural and functional information of the enzyme. The enzyme plays several interlinked biological functions and there is an urgent need to interpret its key active-site residues to infer function and establish role. The human protein q96c10.1 is annotated using tools such as interpro, go and cdd. The physicochemical properties are estimated using the tool protparam. We describe the enzyme protein model developed using modeller to identify active site residues. We used consurf to estimate the structural conservation and is evolutionary relationship is inferred using known close sequence homologs. The active site is predicted using castp and its topological flexibility is estimated through cabs-flex. The protein is annotated as a hydrolase using available data and ddx58 is found as its top-ranked interacting protein partner. We show that about 124 residues are found to be highly conserved among 259 homologs, clustered in 7 clades with the active-site showing low sequence conservation. It is further shown that only 9 loci among the 42 active-site residues are conserved with limited structural fluctuation from the wild type structure. Thus, we document various useful information linked to function, sequence similarity and phylogeny of the enzyme for annotation as potential helicase as designated by uniprot. Data shows limited degree of conserved sequence segments with topological flexibility unlike in other subfamily members of the protein.
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Affiliation(s)
- Vandana Kamjula
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
| | - Ananya Kanneganti
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
| | - Rohan Metla
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
| | - Kusuma Nidamanuri
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
| | - Sudarshan Idupulapati
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
| | - Ashish Runthala
- Department of Biotechnology, Koneru Lakshmaiah Education Foundation, Vaddeswaram, AP, India
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6
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Ritter SPA, Lewis AC, Vincent SL, Lo LL, Cunha APA, Chamot D, Ensminger I, Espie GS, Owttrim GW. Evidence for convergent sensing of multiple abiotic stresses in cyanobacteria. Biochim Biophys Acta Gen Subj 2019; 1864:129462. [PMID: 31669584 DOI: 10.1016/j.bbagen.2019.129462] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 09/18/2019] [Accepted: 09/20/2019] [Indexed: 02/06/2023]
Abstract
BACKGROUND Bacteria routinely utilize two-component signal transduction pathways to sense and alter gene expression in response to environmental cues. While cyanobacteria express numerous two-component systems, these pathways do not regulate all of the genes within many of the identified abiotic stress-induced regulons. METHODS Electron transport inhibitors combined with western analysis and measurement of chlorophyll a fluorescent yield, using pulse amplitude modulation fluorometry, were used to detect the effect of a diverse range of abiotic stresses on the redox status of the photosynthetic electron transport chain and the accumulation and degradation of the Synechocystis sp. PCC 6803 DEAD box RNA helicase, CrhR. RESULTS Alterations in CrhR abundance were tightly correlated with the redox poise of the electron transport chain between QA and cytochrome b6f, with reduction favoring CrhR accumulation. CONCLUSIONS The results provide evidence for an alternative, convergent sensing mechanism mediated through the redox poise of QB/PQH2 that senses multiple, divergent forms of abiotic stress and regulates accumulation of CrhR. The RNA helicase activity of CrhR could then function as a post-translational effector to regulate downstream gene expression. GENERAL SIGNIFICANCE The potential for a related system in Staphylococcus aureus and higher plant chloroplasts suggest convergent sensing mechanisms may be evolutionarily conserved and occur more widely than anticipated.
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Affiliation(s)
- Sean P A Ritter
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Allison C Lewis
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, Dresden 01307, Germany.
| | - Shelby L Vincent
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Li Ling Lo
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | | | - Danuta Chamot
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - Ingo Ensminger
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - George S Espie
- Department of Cell and Systems Biology, University of Toronto, Mississauga, ON L5L 1C6, Canada
| | - George W Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
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7
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Playter T, Konhauser K, Owttrim GW, Whitford DS, Warchola T, Hodgson C, Mloszewska AM, Sutherland B, Zonneveld JP, Pemberton SG, Gingras MK. Determination of the Settling Rate of Clay/Cyanobacterial Floccules. J Vis Exp 2018. [PMID: 29939174 DOI: 10.3791/57176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The mechanisms underpinning the deposition of fine-grained, organic-rich sediments are still largely debated. Specifically, the impact of the interaction of clay particles with reactive, planktonic cyanobacterial cells to the sedimentary record is under studied. This interaction is a potentially major contributor to shale depositional models. Within a lab setting, the flocculation and sedimentation rates of these materials can be examined and measured in a controlled environment. Here, we detail a protocol for measuring the sedimentation rate of cyanobacterial/clay mixtures. This methodology is demonstrated through the description of two sample experiments: the first uses kaolin (a dehydrated form of kaolinite) and Synechococcus sp. PCC 7002 (a marine coccoid cyanobacteria), and the second uses kaolin and Synechocystis sp. PCC 6803 (a freshwater coccoid cyanobacteria). Cyanobacterial cultures are mixed with varying amounts of clay within a specially designed tank apparatus optimized to allow continuous, real-time video and photographic recording. The sampling procedures are detailed as well as a post-collection protocol for precise measurement of chlorophyll a from which the concentration of cyanobacterial cells remaining in suspension can be determined. Through experimental replication, a profile is constructed that displays sedimentation rate.
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Affiliation(s)
- Tiffany Playter
- Department of Earth and Atmospheric Sciences, University of Alberta;
| | - Kurt Konhauser
- Department of Earth and Atmospheric Sciences, University of Alberta
| | | | | | - Tyler Warchola
- Department of Earth and Atmospheric Sciences, University of Alberta
| | - Cheryl Hodgson
- Department of Earth and Atmospheric Sciences, University of Alberta; Department of Earth Sciences, Simon Fraser University
| | | | - Bruce Sutherland
- Department of Earth and Atmospheric Sciences, University of Alberta
| | - J-P Zonneveld
- Department of Earth and Atmospheric Sciences, University of Alberta
| | | | - Murray K Gingras
- Department of Earth and Atmospheric Sciences, University of Alberta
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8
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Cyanobacterial RNA Helicase CrhR Localizes to the Thylakoid Membrane Region and Cosediments with Degradosome and Polysome Complexes in Synechocystis sp. Strain PCC 6803. J Bacteriol 2016; 198:2089-99. [PMID: 27215789 DOI: 10.1128/jb.00267-16] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 05/20/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The cyanobacterium Synechocystis sp. strain PCC 6803 encodes a single DEAD box RNA helicase, CrhR, whose expression is tightly autoregulated in response to cold stress. Subcellular localization and proteomic analysis results indicate that CrhR localizes to both the cytoplasmic and thylakoid membrane regions and cosediments with polysome and RNA degradosome components. Evidence is presented that either functional RNA helicase activity or a C-terminal localization signal was required for polysome but not thylakoid membrane localization. Polysome fractionation and runoff translation analysis results indicate that CrhR associates with actively translating polysomes. The data implicate a role for CrhR in translation or RNA degradation in the thylakoid region related to thylakoid biogenesis or stability, a role that is enhanced at low temperature. Furthermore, CrhR cosedimentation with polysome and RNA degradosome complexes links alteration of RNA secondary structure with a potential translation-RNA degradation complex in Synechocystis IMPORTANCE The interaction between mRNA translation and degradation is a major determinant controlling gene expression. Regulation of RNA function by alteration of secondary structure by RNA helicases performs crucial roles, not only in both of these processes but also in all aspects of RNA metabolism. Here, we provide evidence that the cyanobacterial RNA helicase CrhR localizes to both the cytoplasmic and thylakoid membrane regions and cosediments with actively translating polysomes and RNA degradosome components. These findings link RNA helicase alteration of RNA secondary structure with translation and RNA degradation in prokaryotic systems and contribute to the data supporting the idea of the existence of a macromolecular machine catalyzing these reactions in prokaryotic systems, an association hitherto recognized only in archaea and eukarya.
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9
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Kopf M, Hess WR. Regulatory RNAs in photosynthetic cyanobacteria. FEMS Microbiol Rev 2015; 39:301-15. [PMID: 25934122 PMCID: PMC6596454 DOI: 10.1093/femsre/fuv017] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Revised: 01/06/2015] [Accepted: 03/10/2015] [Indexed: 12/02/2022] Open
Abstract
Regulatory RNAs play versatile roles in bacteria in the coordination of gene expression during various physiological processes, especially during stress adaptation. Photosynthetic bacteria use sunlight as their major energy source. Therefore, they are particularly vulnerable to the damaging effects of excess light or UV irradiation. In addition, like all bacteria, photosynthetic bacteria must adapt to limiting nutrient concentrations and abiotic and biotic stress factors. Transcriptome analyses have identified hundreds of potential regulatory small RNAs (sRNAs) in model cyanobacteria such as Synechocystis sp. PCC 6803 or Anabaena sp. PCC 7120, and in environmentally relevant genera such as Trichodesmium, Synechococcus and Prochlorococcus. Some sRNAs have been shown to actually contain μORFs and encode short proteins. Examples include the 40-amino-acid product of the sml0013 gene, which encodes the NdhP subunit of the NDH1 complex. In contrast, the functional characterization of the non-coding sRNA PsrR1 revealed that the 131 nt long sRNA controls photosynthetic functions by targeting multiple mRNAs, providing a paradigm for sRNA functions in photosynthetic bacteria. We suggest that actuatons comprise a new class of genetic elements in which an sRNA gene is inserted upstream of a coding region to modify or enable transcription of that region.
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Affiliation(s)
- Matthias Kopf
- Faculty of Biology, Institute of Biology III, University of Freiburg, D-79104 Freiburg, Germany
| | - Wolfgang R Hess
- Faculty of Biology, Institute of Biology III, University of Freiburg, D-79104 Freiburg, Germany
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10
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Conditional, temperature-induced proteolytic regulation of cyanobacterial RNA helicase expression. J Bacteriol 2014; 196:1560-8. [PMID: 24509313 DOI: 10.1128/jb.01362-13] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Conditional proteolysis is a crucial process regulating the abundance of key regulatory proteins associated with the cell cycle, differentiation pathways, or cellular response to abiotic stress in eukaryotic and prokaryotic organisms. We provide evidence that conditional proteolysis is involved in the rapid and dramatic reduction in abundance of the cyanobacterial RNA helicase, CrhR, in response to a temperature upshift from 20 to 30°C. The proteolytic activity is not a general protein degradation response, since proteolysis is only present and/or functional in cells grown at 30°C and is only transiently active at 30°C. Degradation is also autoregulatory, since the CrhR proteolytic target is required for activation of the degradation machinery. This suggests that an autoregulatory feedback loop exists in which the target of the proteolytic machinery, CrhR, is required for activation of the system. Inhibition of translation revealed that only elongation is required for induction of the temperature-regulated proteolysis, suggesting that translation of an activating factor was already initiated at 20°C. The results indicate that Synechocystis responds to a temperature shift via two independent pathways: a CrhR-independent sensing and signal transduction pathway that regulates induction of crhR expression at low temperature and a CrhR-dependent conditional proteolytic pathway at elevated temperature. The data link the potential for CrhR RNA helicase alteration of RNA secondary structure with the autoregulatory induction of conditional proteolysis in the response of Synechocystis to temperature upshift.
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11
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Rosana ARR, Chamot D, Owttrim GW. Autoregulation of RNA helicase expression in response to temperature stress in Synechocystis sp. PCC 6803. PLoS One 2012; 7:e48683. [PMID: 23119089 PMCID: PMC3485376 DOI: 10.1371/journal.pone.0048683] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Accepted: 09/28/2012] [Indexed: 12/12/2022] Open
Abstract
RNA helicases are ubiquitous enzymes whose modification of RNA secondary structure is known to regulate RNA function. The pathways controlling RNA helicase expression, however, have not been well characterized. Expression of the cyanobacterial RNA helicase, crhR, is regulated in response to environmental signals that alter the redox poise of the electron transport chain, including light and temperature. Here we analyze crhR expression in response to alteration of abiotic conditions in wild type and a crhR mutant, providing evidence that CrhR autoregulates its own expression through a combination of transcriptional and post-transcriptional mechanisms. Temperature regulates crhR expression through alteration of both transcript and protein half-life which are significantly extended at low temperature (20°C). CrhR-dependent mechanisms regulate both the transient accumulation of crhR transcript at 20°C and stability of the CrhR protein at all temperatures. CrhR-independent mechanisms regulate temperature sensing and induction of crhR transcript accumulation at 20°C and the temperature regulation of crhR transcript stability, suggesting CrhR is not directly associated with crhR mRNA turnover. Many of the processes are CrhR- and temperature-dependent and occur in the absence of a correlation between crhR transcript and protein abundance. The data provide important insights into not only how RNA helicase gene expression is regulated but also the role that rearrangement of RNA secondary structure performs in the molecular response to temperature stress. We propose that the crhR-regulatory pathway exhibits characteristics similar to the heat shock response rather than a cold stress-specific mechanism.
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Affiliation(s)
| | - Danuta Chamot
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
| | - George W. Owttrim
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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