scholarly journals Random mutagenesis of bacterial luciferase: critical role of Glu175 in the control of luminescence decay

2005 ◽  
Vol 385 (2) ◽  
pp. 575-580 ◽  
Author(s):  
Saman HOSSEINKHANI ◽  
Rose SZITTNER ◽  
Edward A. MEIGHEN
Keyword(s):  
Decay Rate ◽  
Random Mutagenesis ◽  
Luminescence Decay ◽  
Decay Rates ◽  
Single Mutation ◽  
Fast Decay ◽  
Rapid Decay ◽  
Slow Decay ◽  
Critical Residue

Bacterial luciferases (LuxAB) can be readily classed as slow or fast decay luciferases based on their rates of luminescence decay in a single turnover assay. Luciferases from Vibrio harveyi and Xenorhabdus (Photorhabdus) luminescens have slow decay rates, and those from the Photobacterium genus, such as Photobacterium fisheri, P. phosphoreum and P. leiognathi, have rapid decay rates. By substitution of a 67-amino-acid stretch of P. phosphoreum LuxA in the central region of the LuxA subunit, the ‘slow’ X. luminescens luciferase was converted into a chimaeric luciferase with a significantly more rapid decay rate [Valkova, Szittner and Meighen (1999) Biochemistry 38, 13820–13828]. To understand better the role of specific residues in the classification of luciferases as slow and fast decay, we have conducted random mutagenesis on this region. One of the mutants generated by a single mutation on LuxA at position 175 [E175G (Glu175→Gly)] resulted in the ‘slow decay’ X. luminescens luciferase being converted into a luciferase with a significantly more rapid decay rate. These results indicate the importance of Glu175 in LuxA as a critical residue for differentiating between ‘slow’ and ‘fast’ luciferases and show that this distinction is primarily due to differences in aldehyde affinity and in the decomposition of the luciferase–flavin–oxygen intermediate.

scholarly journals Role of Intracellular Na+ in the Regulation of [Ca2+]i in the Rat Suprachiasmatic Nucleus Neurons

2019 ◽  
Vol 20 (19) ◽  
pp. 4868
Author(s):  
Ruo-Ciao Cheng ◽  
Pi-Cheng Cheng ◽  
Yi-Chi Wang ◽  
Rong-Chi Huang
Keyword(s):  
Decay Rate ◽  
Suprachiasmatic Nucleus ◽  
Cardiac Glycoside ◽  
Spontaneous Firing ◽  
Fast Decay ◽  
Slow Decay ◽  
Central Clock ◽  
Ca2 Channels ◽  
Ionophore Monensin

Transmembrane Ca2+ influx is essential to the proper functioning of the central clock in the suprachiasmatic nucleus (SCN). In the rat SCN neurons, the clearance of somatic Ca2+ following depolarization-induced Ca2+ transients involves Ca2+ extrusion via Na+/Ca2+ exchanger (NCX) and mitochondrial Ca2+ buffering. Here we show an important role of intracellular Na+ in the regulation of [Ca2+]i in these neurons. The effect of Na+ loading on [Ca2+]i was determined with the Na+ ionophore monensin and the cardiac glycoside ouabain to block Na+/K+-ATPase (NKA). Ratiometric Na+ and Ca2+ imaging was used to measure the change in [Na+]i and [Ca2+]i, and cell-attached recordings to investigate the effects of monensin and ouabain on spontaneous firing. Our results show that in spite of opposite effects on spontaneous firing and basal [Ca2+], both monensin and ouabain induced Na+ loading, and increased the peak amplitude, slowed the fast decay rate, and enhanced the slow decay phase of 20 mM K+-evoked Ca2+ transients. Furthermore, both ouabain and monensin preferentially enhanced nimodipine-insensitive Ca2+ transients. Together, our results indicate that in the SCN neurons the NKA plays an important role in regulating [Ca2+]i, in particular, associated with nimodipine-insensitive Ca2+ channels.

Fast scalar decay in a shear flow: modes and pseudomodes

2007 ◽  
Vol 572 ◽  
pp. 219-229 ◽  
Author(s):  
J. VANNESTE ◽  
J. G. BYATT-SMITH
Keyword(s):  
Shear Flow ◽  
Eigenvalue Problem ◽  
Decay Rate ◽  
Shear Flows ◽  
Passive Scalar ◽  
Decay Rates ◽  
Constant Speed ◽  
Fast Decay ◽  
Small Noise ◽  
Stream Direction

The decay of a passive scalar in a sinusoidal shear flow translating in the cross-stream direction at a constant speed u is studied in the limit of small diffusivity κ. The decay rate, obtained by solving an eigenvalue problem, is found to tend to a non-zero constant as κ→0 when u is of order κ1/2. This result, establishing that fast decay is possible in shear flows, is fragile however: because of the existence of pseudomodes, the addition of a small noise leads to decay rates that decrease to zero with κ as κ2/5.

scholarly journals The range of linguistic units: Distance effects in English mandative subjunctive constructions

2019 ◽  
Vol 56 (2) ◽  
pp. 231-268
Author(s):  
THOMAS BERG ◽  
TIM ZINGLER ◽  
ARNE LOHMANN
Keyword(s):  
Decay Rate ◽  
Decision Process ◽  
Language Production ◽  
Empirical Test ◽  
Decay Rates ◽  
Test Case ◽  
Structural Hierarchy ◽  
Distance Effects ◽  
Linguistic Units

This study examines the role of distance in the decision among grammatical variants. The empirical test case is the English mandative subjunctive construction, which co-occurs with an embedded modal auxiliary, a subjunctive or an indicative verb form. The fact that the subjunctive is triggered by specific lexical items allows one to measure the distance between the triggering unit and the target verb. This distance is found to play a significant role in the grammatical decision process. With increasing distance between trigger and target, the probability of selecting a modal auxiliary increases and the probability of selecting the subjunctive decreases. The theoretical account hinges on the range and strength of linguistic units. Syntactic units (i.e. modals) are claimed to have a wider range than morphological units (i.e. indicative and subjunctive). Furthermore, the indicative is claimed to have a wider range than the subjunctive. Varying ranges are interpreted as varying decay rates. The lower decay rate of syntactic as compared to morphological units results from the syntactic level being superordinated to the morphological level in language production. The inclusion of the semantic and the phonological levels confirms that the position of a level in the structural hierarchy determines its range.

scholarly journals Enhanced production of Clavulanic acid by improving glycerol utilization using reporter-guided mutagenesis of an industrial Streptomyces clavuligerus strain

2021 ◽  
Author(s):  
Chang-Hun Shin ◽  
Hang Soo Cho ◽  
Hyung-Jin Won ◽  
Ho Jeong Kwon ◽  
Chan-Wha Kim ◽  
...  
Keyword(s):  
Clavulanic Acid ◽  
Wild Type Strain ◽  
Random Mutagenesis ◽  
Streptomyces Clavuligerus ◽  
Wild Type ◽  
Mutant Selection ◽  
Enhanced Production ◽  
Industrial Strains ◽  
Glycerol Utilization

Abstract Clavulanic acid (CA) produced by Streptomyces clavuligerus is a clinically important β-lactamase inhibitor. It is known that glycerol utilization can significantly improve cell growth and CA production of S. clavuligerus. We found that the industrial CA-producing S. clavuligerus strain OR generated by random mutagenesis consumes less glycerol than the wild-type strain; we then developed a mutant strain in which the glycerol utilization operon is overexpressed, as compared to the parent OR strain, through iterative random mutagenesis and reporter-guided selection. The CA production of the resulting S. clavuligerus ORUN strain was increased by approximately 31.3 per cent (5.21 ± 0.26 g/L) in a flask culture and 17.4 per cent (6.11 ± 0.36 g/L) in a fermenter culture, as compared to that of the starting OR strain. These results confirmed the important role of glycerol utilization in CA production and demonstrated that reporter-guided mutant selection is an efficient method for further improvement of randomly mutagenized industrial strains.

scholarly journals The Population Genetics of Synthetic Lethals

Genetics ◽  
1998 ◽  
Vol 150 (1) ◽  
pp. 449-458 ◽  
Author(s):  
Patrick C Phillips ◽  
Norman A Johnson
Keyword(s):  
Double Mutant ◽  
Single Locus ◽  
Single Mutation ◽  
Hybrid Breakdown ◽  
Selection Coefficient ◽  
Deleterious Alleles ◽  
Synthetic Lethals ◽  
Mutant Homozygote ◽  
Diploid Model

Abstract Synthetic lethals are variants at different loci that have little or no effect on viability singly but cause lethality in combination. The importance of synthetic lethals and, more generally, of synthetic deleterious loci (SDL) has been controversial. Here, we derive the expected frequencies for SDL under a mutation-selection balance for the complete haploid model and selected cases of the diploid model. We have also obtained simple approximations that demonstrate good fit to exact solutions based on numerical iterations. In the haploid case, equilibrium frequencies of carrier haplotypes (individuals with only a single mutation) are comparable to analogous single-locus results, after allowing for the effects of linkage. Frequencies in the diploid case, however, are much higher and more comparable to the square root of the single-locus results. In particular, when selection operates only on the double-mutant homozygote and linkage is not too tight, the expected frequency of the carriers is approximately the quartic root of the ratio between the mutation rate and the selection coefficient of the synthetics. For a reasonably wide set of models, the frequencies of carriers can be on the order of a few percent. The equilibrium frequencies of these deleterious alleles can be relatively high because, with SDL, both dominance and epistasis act to shield carriers from exposure to selection. We also discuss the possible role of SDL in maintaining genetic variation and in hybrid breakdown.

Notizen:Phosphorescence Decay in Thallium-Doped Ammonium Chloride

1978 ◽  
Vol 33 (10) ◽  
pp. 1241-1242 ◽  
Author(s):  
S. Chaudhari ◽  
T. R. Joshi ◽  
R. V. Joshi
Keyword(s):  
Aqueous Solution ◽  
Ammonium Chloride ◽  
Mechanical Treatment ◽  
Room Temperature ◽  
Host Lattice ◽  
Luminescence Decay ◽  
Decay Rates ◽  
Negative Ion ◽  
Ultraviolet Emission ◽  
Near Ultraviolet

Abstract The phosphorescence decay rates of thallium-doped ammonium chloride (NH4Cl:Tl) phosphors, prepared by crystallization from aqueous solution, have been studied at room temperature for near-ultraviolet emission. The effects of impurity concentration as well as thermal and/or mechanical treatment on the decay rates have been examined. Phosphorescence centres consisting of a Tl+ion and a nearby negative ion vacancy are suggested to be responsible for the observed luminescence decay. The changes in the decay characteristics after pretreatments are explained on the basis of the location of the centres in normal and distorted regions of the host lattice.

Role of the adenovirus 72-kDa DNA binding protein in the rapid decay of early viral mRNA

Virology ◽  
1988 ◽  
Vol 165 (2) ◽  
pp. 438-445 ◽  
Author(s):  
Ianis Lazaridis ◽  
Alexander Babich ◽  
Joseph R. Nevins
Keyword(s):  
Dna Binding ◽  
Binding Protein ◽  
Dna Binding Protein ◽  
Viral Mrna ◽  
Rapid Decay

scholarly journals On the interpretation of annual oscillations in 32Si and 36Cl decay rate measurements

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Pommé ◽  
K. Pelczar ◽  
K. Kossert ◽  
I. Kajan
Keyword(s):  
Decay Rate ◽  
Solar Neutrino ◽  
National Laboratory ◽  
Neutrino Flux ◽  
Measurement Data ◽  
Brookhaven National Laboratory ◽  
Decay Rates ◽  
Dew Point ◽  
Annual Variations ◽  
Set Up

AbstractThe 32Si decay rate measurement data of Alburger et al. obtained in 1982–1986 at Brookhaven National Laboratory have been presented repeatedly as evidence for solar neutrino-induced beta decay. The count rates show an annual sinusoidal oscillation of about 0.1% amplitude and maximum at February–March. Several authors have claimed that the annual oscillations could not be explained by environmental influences on the set-up, and they questioned the invariability of the decay constant. They hypothesised a correlation with changes in the solar neutrino flux due to annual variations in the Earth-Sun distance, in spite of an obvious mismatch in amplitude and phase. In this work, environmental conditions at the time of the experiment are presented. The 32Si decay rate measurements appear to be inversely correlated with the dew point in a nearby weather station. Susceptibility of the detection set-up to local temperature and humidity conditions is a likely cause of the observed instabilities in the measured decay rates. Similar conclusions apply to 36Cl decay rates measured at Ohio State University in 2005–2012.

On the optimality of optical pumping for a closed Λ-system with large decay rates of the intermediate excited state

2021 ◽  
Author(s):  
Dionisis Stefanatos ◽  
Emmanuel Paspalakis
Keyword(s):  
Optimal Control ◽  
Excited State ◽  
Decay Rate ◽  
Optimal Control Theory ◽  
Optical Pumping ◽  
Quantum Information Processing ◽  
Decay Rates ◽  
Population Transfer ◽  
Initial State ◽  
Weakly Coupled

Abstract We use optimal control theory to show that for a closed Λ-system where the excited intermediate level decays to the lower levels with a common large rate, the optimal scheme for population transfer between the lower levels is actually optical pumping. In order to obtain this result we exploit the large decay rate to eliminate adiabatically the weakly coupled excited state, then perform a transformation to the basis comprised of the dark and bright states, and finally apply optimal control to this transformed system. Subsequently, we confirm the optimality of the optical pumping scheme for the original closed Λ-system using numerical optimal control. We also demonstrate numerically that optical pumping remains optimal when the decay rate to the target state is larger than that to the initial state or the two rates are not very different from each other. The present work is expected to find application in various tasks of quantum information processing, where such systems are encountered

scholarly journals Decay of Fecal Indicator Bacterial Populations and Bovine-Associated Source-Tracking Markers in Freshly Deposited Cow Pats

2013 ◽  
Vol 80 (1) ◽  
pp. 110-118 ◽  
Author(s):  
Adelumola Oladeinde ◽  
Thomas Bohrmann ◽  
Kelvin Wong ◽  
S. T. Purucker ◽  
Ken Bradshaw ◽  
...  
Keyword(s):  
Decay Rate ◽  
Fecal Indicator Bacteria ◽  
Decay Rates ◽  
Indicator Bacteria ◽  
Source Tracking ◽  
Fecal Indicator ◽  
Bacterial Populations ◽  
Content Type ◽  
E Coli ◽  
Decay Dynamic

ABSTRACTUnderstanding the survival of fecal indicator bacteria (FIB) and microbial source-tracking (MST) markers is critical to developing pathogen fate and transport models. Although pathogen survival in water microcosms and manure-amended soils is well documented, little is known about their survival in intact cow pats deposited on pastures. We conducted a study to determine decay rates of fecal indicator bacteria (Escherichia coliand enterococci) and bovine-associated MST markers (CowM3, Rum-2-bac, and GenBac) in 18 freshly deposited cattle feces from three farms in northern Georgia. Samples were randomly assigned to shaded or unshaded treatment in order to determine the effects of sunlight, moisture, and temperature on decay rates. A general linear model (GLM) framework was used to determine decay rates. Shading significantly decreased the decay rate of theE. colipopulation (P< 0.0001), with a rate of −0.176 day−1for the shaded treatment and −0.297 day−1for the unshaded treatment. Shading had no significant effect on decay rates of enterococci, CowM3, Rum-2-bac, and GenBac (P> 0.05). In addition,E. colipopulations showed a significant growth rate (0.881 day−1) in the unshaded samples during the first 5 days after deposition. UV-B was the most important parameter explaining the decay rate ofE. colipopulations. A comparison of the decay behaviors among all markers indicated that enterococcus concentrations exhibit a better correlation with the MST markers thanE. coliconcentrations. Our results indicate that bovine-associated MST markers can survive in cow pats for at least 1 month after excretion, and although their decay dynamic differs from the decay dynamic ofE. colipopulations, they seem to be reliable markers to use in combination with enterococci to monitor fecal pollution from pasture lands.

Sign in / Sign up

Export Citation Format

Share Document