scholarly journals Degradation of Lon in Caulobacter crescentus

2020 ◽  
Vol 203 (1) ◽  
Author(s):  
Benjamin B. Barros ◽  
Samar A. Mahmoud ◽  
Peter Chien ◽  
Rilee D. Zeinert
Keyword(s):  
Caulobacter Crescentus ◽  
Feedback Mechanism ◽  
Transcriptional Level ◽  
Lon Protease ◽  
Content Type ◽  
Low Levels ◽  
Critical Machines ◽  
Carboxy Terminal ◽  
Replication Initiator ◽  
Proteolytic Capacity

ABSTRACT Protein degradation is an essential process in all organisms. This process is irreversible and energetically costly; therefore, protein destruction must be tightly controlled. While environmental stresses often lead to upregulation of proteases at the transcriptional level, little is known about posttranslational control of these critical machines. In this study, we show that in Caulobacter crescentus levels of the Lon protease are controlled through proteolysis. Lon turnover requires active Lon and ClpAP proteases. We show that specific determinants dictate Lon stability with a key carboxy-terminal histidine residue driving recognition. Expression of stabilized Lon variants results in toxic levels of protease that deplete normal Lon substrates, such as the replication initiator DnaA, to lethally low levels. Taken together, results of this work demonstrate a feedback mechanism in which ClpAP and Lon collaborate to tune Lon proteolytic capacity for the cell. IMPORTANCE Proteases are essential, but unrestrained activity can also kill cells by degrading essential proteins. The quality-control protease Lon must degrade many misfolded and native substrates. We show that Lon is itself controlled through proteolysis and that bypassing this control results in toxic consequences for the cell.

scholarly journals Degradation of Lon in Caulobacter crescentus

2020 ◽  
Author(s):  
Benjamin B Barros ◽  
Samar A Mahmoud ◽  
Peter Chien ◽  
Rilee D. Zeinert
Keyword(s):  
Translational Control ◽  
Caulobacter Crescentus ◽  
Feedback Mechanism ◽  
Transcriptional Level ◽  
Lon Protease ◽  
Low Levels ◽  
Critical Machines ◽  
Carboxy Terminal ◽  
Replication Initiator ◽  
Proteolytic Capacity

AbstractProtein degradation is an essential process in all organisms. This process is irreversible and energetically costly; therefore, protein destruction must be tightly controlled. While environmental stresses often lead to upregulation of proteases at the transcriptional level, little is known about post-translational control of these critical machines. In this study we show that in Caulobacter crescentus levels of the Lon protease are controlled through proteolysis. Lon turnover requires active Lon and ClpAP proteases. We show that specific determinants dictate Lon stability with a key carboxy-terminal histidine residue driving recognition. Expression of stabilized Lon variants results in toxic levels of protease that deplete normal Lon substrates such as the replication initiator DnaA to lethally low levels. Taken together, this work demonstrates a feedback mechanism in which ClpAP and Lon collaborate to tune Lon proteolytic capacity for the cell.ImportanceProteases are essential, but unrestrained activity can also kill cells by degrading essential proteins. The quality control protease Lon must degrade many misfolded and native substrates. We show that Lon is itself controlled through proteolysis and that bypassing this control results in toxic consequences for the cell.

scholarly journals Lon recognition of the replication initiator DnaA is not confined to a single degron

2018 ◽  
Author(s):  
Jing Liu ◽  
Laura Francis ◽  
Peter Chien
Keyword(s):  
Acute Stress ◽  
Caulobacter Crescentus ◽  
Initiation Site ◽  
Active State ◽  
Lon Protease ◽  
Species Specific ◽  
Replication Initiator

SummaryDnaA initiates chromosome replication in bacteria. In Caulobacter crescentus, the Lon protease degrades DnaA to coordinate replication with nutrient availability and to halt the cell cycle during acute stress. Here we characterize the mechanism of DnaA recognition by Lon. We find that the native folded state of DnaA is crucial for its degradation, in contrast to the well-known role of Lon in degrading misfolded proteins. We fail to identify a single degradation motif (degron) sufficient for DnaA degradation, rather we show that both the ATPase domain and a species-specific N-terminal motif are important for productive Lon degradation of DnaA. Mutations in either of these determinants disrupt DnaA degradation in vitro and in vivo. DnaA switches from an inactive to active state depending on its nucleotide state and we find that locking DnaA in an active state inhibits degradation. Our working model is that Lon engages DnaA through at least two elements, one of which anchors DnaA to Lon and the other acting as an initiation site for degradation.

When do job insecure employees adapt to change?

2019 ◽  
Vol 25 (3) ◽  
pp. 271-286 ◽  
Author(s):  
Kristi N. Lavigne ◽  
Victoria L. Whitaker ◽  
Dustin K. Jundt ◽  
Mindy K. Shoss
Keyword(s):  
Job Insecurity ◽  
Small Sample ◽  
Adaptive Performance ◽  
Work Behaviors ◽  
Content Type ◽  
Work Tasks ◽  
Main Effect ◽  
Low Levels ◽  
The Impact ◽  
The Relationship

Purpose The purpose of this paper is to examine the relationship between job insecurity and adaptive performance (AP), contingent on changes to core work tasks, which we position as a situational cue to employees regarding important work behaviors. Design/methodology/approach Employees and their supervisors were invited to participate in the study. Supervisors were asked to provide ratings of employees’ AP and changes to core tasks; employees reported on job insecurity. Findings As predicted, changes to core tasks moderated the relationship between job insecurity and AP. Job insecurity was negatively related to AP for those experiencing low levels of change, but was not related to AP for those experiencing high levels of change. Counter to expectations, no main effect of job insecurity was found. Research limitations/implications This study employed a fairly small sample of workers from two organizations, which could limit generalizability. Practical implications The study identifies changes to core tasks as a boundary condition for the job insecurity–AP relationship. Findings suggest that organizations may not observe deleterious consequences of job insecurity on AP when changes to core tasks are high. Originality/value Few researchers have examined boundary conditions of the impact of job insecurity on AP. Furthermore, inconsistent findings regarding the link between job insecurity and AP have emerged. This study fills the gap and expands upon previous research by examining changes to core tasks as a condition under which job insecurity does not pose an issue for AP.

Employee emotional displays in the extended service encounter

2019 ◽  
Vol 31 (1) ◽  
pp. 115-136 ◽  
Author(s):  
Magnus Soderlund ◽  
Hanna Berg
Keyword(s):  
Marketing Communications ◽  
Emotional Expressions ◽  
Service Firms ◽  
Still Images ◽  
Content Type ◽  
Emotional Displays ◽  
Service Setting ◽  
Low Levels ◽  
The Impact ◽  
Practical Implications

Purpose The purpose of this paper is to examine the impact of happiness expressed by service firm employees when they are depicted in marketing communications materials, such as printed ads and videos. Design/methodology/approach Two experiments were conducted in a fitness service setting, in which employee display of happiness was manipulated (low vs high). Findings Both experiments showed that expressions of high levels of happiness produced a more positive attitude toward the service employee than expressions of low levels of happiness. Moreover, the impact of the expression of happiness on the evaluation of the employee was mediated by several variables, which suggests that the influence of depicted employees’ emotional expressions can take several routes. Practical implications The results imply that service firms should not only be mindful about which specific employee they select for appearing in marketing communications materials, they should also pay attention to the emotional displays of selected employees. Originality/value The present study contributes to previous research by assessing a set of potential mediators to explain why displays of happiness influence consumers, and by examining these effects in a marketing communications setting in which the customer is exposed to still images or video-based representations of the employee. The present study also focuses explicitly on happiness rather than on smiles.

scholarly journals Association of the Cold Shock DEAD-Box RNA Helicase RhlE to the RNA Degradosome in Caulobacter crescentus

2017 ◽  
Vol 199 (13) ◽  
Author(s):  
Angel A. Aguirre ◽  
Alexandre M. Vicente ◽  
Steven W. Hardwick ◽  
Daniela M. Alvelos ◽  
Ricardo R. Mazzon ◽  
...  
Keyword(s):  
Low Temperature ◽  
Caulobacter Crescentus ◽  
Immunoblot Analysis ◽  
Rna Helicase ◽  
Rnase E ◽  
Rna Helicases ◽  
Content Type ◽  
Dead Box ◽  
Rna Degradosome ◽  
The Dead

ABSTRACT In diverse bacterial lineages, multienzyme assemblies have evolved that are central elements of RNA metabolism and RNA-mediated regulation. The aquatic Gram-negative bacterium Caulobacter crescentus, which has been a model system for studying the bacterial cell cycle, has an RNA degradosome assembly that is formed by the endoribonuclease RNase E and includes the DEAD-box RNA helicase RhlB. Immunoprecipitations of extracts from cells expressing an epitope-tagged RNase E reveal that RhlE, another member of the DEAD-box helicase family, associates with the degradosome at temperatures below those optimum for growth. Phenotype analyses of rhlE, rhlB, and rhlE rhlB mutant strains show that RhlE is important for cell fitness at low temperature and its role may not be substituted by RhlB. Transcriptional and translational fusions of rhlE to the lacZ reporter gene and immunoblot analysis of an epitope-tagged RhlE indicate that its expression is induced upon temperature decrease, mainly through posttranscriptional regulation. RNase E pulldown assays show that other proteins, including the transcription termination factor Rho, a second DEAD-box RNA helicase, and ribosomal protein S1, also associate with the degradosome at low temperature. The results suggest that the RNA degradosome assembly can be remodeled with environmental change to alter its repertoire of helicases and other accessory proteins. IMPORTANCE DEAD-box RNA helicases are often present in the RNA degradosome complex, helping unwind secondary structures to facilitate degradation. Caulobacter crescentus is an interesting organism to investigate degradosome remodeling with change in temperature, because it thrives in freshwater bodies and withstands low temperature. In this study, we show that at low temperature, the cold-induced DEAD-box RNA helicase RhlE is recruited to the RNA degradosome, along with other helicases and the Rho protein. RhlE is essential for bacterial fitness at low temperature, and its function may not be complemented by RhlB, although RhlE is able to complement for rhlB loss. These results suggest that RhlE has a specific role in the degradosome at low temperature, potentially improving adaptation to this condition.

scholarly journals Coordination of K+Transporters in Neurospora: TRK1 Is Scarce and Constitutive, while HAK1 Is Abundant and Highly Regulated

2013 ◽  
Vol 12 (5) ◽  
pp. 684-696 ◽  
Author(s):  
Alberto Rivetta ◽  
Kenneth E. Allen ◽  
Carolyn W. Slayman ◽  
Clifford L. Slayman
Keyword(s):  
Atp Hydrolysis ◽  
Model Organism ◽  
Carbon Starvation ◽  
Transmembrane Helices ◽  
Content Type ◽  
Biochemical Genetic ◽  
Low Levels ◽  
Electrophysiological Characterization ◽  
Low K ◽  
Potassium Limitation

ABSTRACTFungi, plants, and bacteria accumulate potassium via two distinct molecular machines not directly coupled to ATP hydrolysis. The first, designated TRK, HKT, or KTR, has eight transmembrane helices and is folded like known potassium channels, while the second, designated HAK, KT, or KUP, has 12 transmembrane helices and resembles MFS class proteins. One of each type functions in the model organismNeurospora crassa, where both are readily accessible for biochemical, genetic, and electrophysiological characterization. We have now determined the operating balance between Trk1p and Hak1p under several important conditions, including potassium limitation and carbon starvation. Growth measurements, epitope tagging, and quantitative Western blotting have shown the geneHAK1to be much more highly regulated than isTRK1. This conclusion follows from three experimental results: (i) Trk1p is expressed constitutively but at low levels, and it is barely sensitive to extracellular [K+] and/or the coexpression ofHAK1; (ii) Hak1p is abundant but is markedly depressed by elevated extracellular concentrations of K+and by coexpression ofTRK1; and (iii) Carbon starvation slowly enhances Hak1p expression and depresses Trk1p expression, yielding steady-state Hak1p:Trk1p ratios of ∼500:1,viz., 10- to 50-fold larger than that in K+- and carbon-replete cells. Additionally, it appears that both potassium transporters can adjust kinetically to sustained low-K+stress by means of progressively increasing transporter affinity for extracellular K+. The underlying observations are (iv) that K+influx via Trk1p remains nearly constant at ∼9 mM/h when extracellular K+is progressively depleted below 0.05 mM and (v) that K+influx via Hak1p remains at ∼3 mM/h when extracellular K+is depleted below 0.1 mM.

Resolution of brain edema in severe brain injury at controlled high and low intracranial pressures

1984 ◽  
Vol 61 (4) ◽  
pp. 707-712 ◽  
Author(s):  
Meihong Cao ◽  
He Lisheng ◽  
Sun Shouzheng
Keyword(s):  
Cerebrospinal Fluid ◽  
Brain Injury ◽  
Brain Edema ◽  
External Ventricular Drainage ◽  
Blue Dye ◽  
Severe Brain Injury ◽  
Content Type ◽  
Intracranial Pressures ◽  
Low Levels ◽  
Cerebrospinal Fluid Protein

✓ A series of 87 patients with severe brain injury were studied. Intracranial pressure (ICP) monitoring and external ventricular drainage were used to control ICP at high and low levels. Clearance of ytterbium-169-labeled diethylenetriaminepentaacetic acid (169Yb-DTPA), Evans blue dye, and ventricular cerebrospinal fluid protein was measured at the two ICP levels over consecutive periods of 4 hours to confirm clearance of brain edema. The results support the hypothesis that brain edema is in part absorbed in the cerebrospinal fluid via transventricular flow.

Directional predictability between returns and volume in cryptocurrencies markets

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Panos Fousekis ◽  
Vasilis Grigoriadis
Keyword(s):  
High Volume ◽  
Stationary Time Series ◽  
Temporal Association ◽  
Informational Efficiency ◽  
Content Type ◽  
Low Levels ◽  
The Cross ◽  
Trading Volumes ◽  
Directional Predictability ◽  
The Empirical Analysis

Purpose This paper aims to identify and quantify directional predictability between returns and volume in major cryptocurrencies markets. Design/methodology/approach The empirical analysis relies on the cross-quantilogram approach that allows one to assess the temporal (lag-lead) association between two stationary time series at different parts of their joint distribution. The data are daily prices and trading volumes from four markets (Bitcoin, Ethereum, Ripple and Litecoin). Findings Extreme returns either positive or negative tend to lead high volume levels. Low levels of trading activity have in general no information content about future returns; high levels, however, tend to precede extreme positive returns. Originality/value This is the first work that uses the cross-quantilogram approach to assess the temporal association between returns and volume in cryptocurrencies markets. The findings provide new insights about the informational efficiency of these markets and the traders’ strategies.

scholarly journals Lon Protease Has Multifaceted Biological Functions inAcinetobacter baumannii

2018 ◽  
Vol 201 (2) ◽  
Author(s):  
Carly Ching ◽  
Brendan Yang ◽  
Chineme Onwubueke ◽  
David Lazinski ◽  
Andrew Camilli ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
Biofilm Formation ◽  
Developmental Process ◽  
Cell Envelope ◽  
Opportunistic Pathogen ◽  
Lon Protease ◽  
Content Type ◽  
Hospital Acquired Infections ◽  
Biofilm Development ◽  
Hospital Acquired

ABSTRACTAcinetobacter baumanniiis a Gram-negative opportunistic pathogen that is known to survive harsh environmental conditions and is a leading cause of hospital-acquired infections. Specifically, multicellular communities (known as biofilms) ofA. baumanniican withstand desiccation and survive on hospital surfaces and equipment. Biofilms are bacteria embedded in a self-produced extracellular matrix composed of proteins, sugars, and/or DNA. Bacteria in a biofilm are protected from environmental stresses, including antibiotics, which provides the bacteria with selective advantage for survival. Although some gene products are known to play roles in this developmental process inA. baumannii, mechanisms and signaling remain mostly unknown. Here, we find that Lon protease inA. baumanniiaffects biofilm development and has other important physiological roles, including motility and the cell envelope. Lon proteases are found in all domains of life, participating in regulatory processes and maintaining cellular homeostasis. These data reveal the importance of Lon protease in influencing keyA. baumanniiprocesses to survive stress and to maintain viability.IMPORTANCEAcinetobacter baumanniiis an opportunistic pathogen and is a leading cause of hospital-acquired infections.A. baumanniiis difficult to eradicate and to manage, because this bacterium is known to robustly survive desiccation and to quickly gain antibiotic resistance. We sought to investigate biofilm formation inA. baumannii, since much remains unknown about biofilm formation in this bacterium. Biofilms, which are multicellular communities of bacteria, are surface attached and difficult to eliminate from hospital equipment and implanted devices. Our research identifies multifaceted physiological roles for the conserved bacterial protease Lon inA. baumannii. These roles include biofilm formation, motility, and viability. This work broadly affects and expands understanding of the biology ofA. baumannii, which will permit us to find effective ways to eliminate the bacterium.

Comparing retail formats in an emerging market

2014 ◽  
Vol 6 (1) ◽  
pp. 48-69 ◽  
Author(s):  
Gordhan K. Saini ◽  
Arvind Sahay
Keyword(s):  
Purchase Intention ◽  
Emerging Market ◽  
Retail Store ◽  
Policy Implications ◽  
Content Type ◽  
Consumer Responses ◽  
Consumer Purchase Intention ◽  
Low Levels ◽  
Low Price Guarantee ◽  
Retail Formats

Purpose – This study aims to examine the importance of credit and low price guarantee (LPG) on consumer purchase intention across types of retail store formats in an emerging market context. Design/methodology/approach – A 2 (kirana/modern retail)×2 (high/low LPG)×2 (credit/no credit) experimental design was used for this study. A sample of 200 respondents was asked about their purchase intention for a newly introduced hypothetical toothpaste brand and six hypotheses were tested. Findings – Findings show that credit and level of LPG determine consumer's purchase intention across store formats. The presence of credit and high LPG increases the purchase intention; however, relatively importance of these two varies by type of store. The absence of credit at kirana store definitely reduces the buying intention, while same is not true for modern retail store, where level of LPG is more important than the credit. Interestingly, buyer is likely to discount high LPG for a month's credit offered by a kirana store. Practical implications – The study can help practitioners and scholars to understand consumer responses to credit and LPG in buying decisions, and subsequently in designing a better product offer at a particular store format in emerging markets. Originality/value – Important insights are provided about the consumer behavior resulting from the presence or absence of credit and high or low levels of LPG in an emerging market context. The study also has public policy implications in a country where FDI in retail is a hotly debated topic.

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