Detrimental Effects of Hypoxia-Specific Expression of Uracil DNA Glycosylase (Ung) in Mycobacterium smegmatis

Mycobacterium tuberculosis is known to reside latently in a significant fraction of the human population. Although the bacterium possesses an aerobic mode of metabolism, it adapts to persistence under hypoxic conditions such as those encountered in granulomas. While in mammalian systems hypoxia is a recognized DNA-damaging stress, aspects of DNA repair in mycobacteria under such conditions have not been studied. We subjected Mycobacterium smegmatis, a model organism, to the Wayne's protocol of hypoxia. Analysis of the mRNA of a key DNA repair enzyme, uracil DNA glycosylase (Ung), by real-time reverse transcriptase PCR (RT-PCR) revealed its downregulation during hypoxia. However, within an hour of recovery of the culture under normal oxygen levels, the Ung mRNA was restored. Analysis of Ung by immunoblotting and enzyme assays supported the RNA analysis results. To understand its physiological significance, we misexpressed Ung in M. smegmatis by using a hypoxia-responsive promoter of narK2 from M. tuberculosis. Although the misexpression of Ung during hypoxia decreased C-to-T mutations, it compromised bacterial survival upon recovery at normal oxygen levels. RT-PCR analysis of other base excision repair gene transcripts (UdgB and Fpg) suggested that these DNA repair functions also share with Ung the phenomenon of downregulation during hypoxia and recovery with return to normal oxygen conditions. We discuss the potential utility of this phenomenon in developing attenuated strains of mycobacteria.

The chemistry of vetivalene-type vetivalene-type naturally-occurring sesquiterpenoids

Vetivalene, 1,4-dimetiiyl-6-isopropylnaphl1tlmlenc(1 ) represents a new sesquiterpene skelcton which 15 presumed to originate from eudesmane by a shift of the angular nicthyl group. Novel sesquiterpenm related to vetivalene have been isolated from plant sources ill ~s c e o ig ears. A suriey dealing xith the chemistry (structure, synthesis and configuration) of members of this interesting new class OF yesquiterpenes, coniprising occidol, risbitinol and the various ernmotinn is presented

The chemistry of vetivalene-type naturally occurring sesqufterpenoids

Vetivalene, 1,4-dimetiiyl-6-isopropylnaphl1tlmlenc(1 ) represents a new sesquiterpene skelcton which 15 presumed to originate from eudesmane by a shift of the angular nicthyl group. Novel sesquiterpenm related to vetivalene have been isolated from plant sources ill ~s c e o ig ears. A suriey dealing xith the chemistry (structure, synthesis and configuration) of members of this interesting new class OF yesquiterpenes, coniprising occidol, risbitinol and the various ernmotinn is presented.

Random-Restart Reactive Tabu Search Algorithm for Detection in Large-MIMO Systems

We present a low-complexity algorithm based on reactive tabu search (RTS) for near maximum likelihood (ML) detection in large-MIMO systems. The conventional RTS algorithm achieves near-ML performance for 4-QAM in large-MIMO systems. But its performance for higher-order QAM is far from ML performance. Here, we propose a random-restart RTS (R3TS) algorithm which achieves significantly better bit error rate (BER) performance compared to that of the conventional RTS algorithm in higher-order QAM. The key idea is to run multiple tabu searches, each search starting with a random initial vector and choosing the best among the resulting solution vectors. A criterion to limit the number of searches is also proposed. Computer simulations show that the R3TS algorithm achieves almost the ML performance in 16 x 16 V-BLAST MIMO system with 16-QAM and 64-QAM at significantly less complexities than the sphere decoder. Also, in a 32 x 32 V-BLAST MIMO system, the R3TS performs close to ML lower bound within 1.6 dB for 16-QAM (128 bps/Hz), and within 2.4 dB for 64-QAM (192 bps/Hz) at 10(-3) BER.

Minimum weight design of fiber-reinforced laminated composite structures with maximum stress and Tsai-Wu failure criteria

In this article, a minimum weight design of carbon/epoxy laminates is carried out using genetic algorithms. New failure envelopes have been developed by the combination of two commonly used phenomenological failure criteria, namely Maximum Stress (MS) and Tsai-Wu (TW) are used to obtain the minimum weight of the laminate. These failure envelopes are the most conservative failure envelope (MCFE) and the least conservative failure envelope (LCFE). Uniaxial and biaxial loading conditions are considered for the study and the differences in the optimal weight of the laminate are compared for the MCFE and LCFE. The MCFE can be used for design of critical load-carrying composites, while the LCFE could be used for the design of composite structures where weight reduction is much more important than safety such as unmanned air vehicles.

High pressure studies on AgI-Ag2O-MoO3 glasses

he effect of pressure on the conductivity of AgI-Ag2 O-MoO3 glasses has been reexamined. A conductivity maximum is observed around 0.7 GPa. No variation of the sample temperature is noted under pressure. The results are found to agree well with the cluster-tissue model.

Layered Tabu Search Algorithm for Large-MIMO Detection and a Lower Bound on ML Performance

In this paper, we are concerned with low-complexity detection in large multiple-input multiple-output (MIMO) systems with tens of transmit/receive antennas. Our new contributions in this paper are two-fold. First, we propose a low-complexity algorithm for large-MIMO detection based on a layered low-complexity local neighborhood search. Second, we obtain a lower bound on the maximum-likelihood (ML) bit error performance using the local neighborhood search. The advantages of the proposed ML lower bound are i) it is easily obtained for MIMO systems with large number of antennas because of the inherent low complexity of the search algorithm, ii) it is tight at moderate-to-high SNRs, and iii) it can be tightened at low SNRs by increasing the number of symbols in the neighborhood definition. Interestingly, the proposed detection algorithm based on the layered local search achieves bit error performances which are quite close to this lower bound for large number of antennas and higher-order QAM. For e. g., in a 32 x 32 V-BLAST MIMO system, the proposed detection algorithm performs close to within 1.7 dB of the proposed ML lower bound at 10(-3) BER for 16-QAM (128 bps/Hz), and close to within 4.5 dB of the bound for 64-QAM (192 bps/Hz).

Modes of binding of α(1–2) linked manno-oligosaccharides to concanavalin A

Three-dimensional structures of the complexes of concanavalin A (ConA) with alpha(1-2) linked mannobiose, triose and tetraose have been generated with the X-ray crystal structure data on native ConA using the CCEM (contact criteria and energy minimization) method. All the constituting mannose residues of the oligosaccharide can reach the primary binding site of ConA (where methyl-alpha-D-mannopyranose binds). However, in all the energetically favoured complexes, either the non-reducing end or middle mannose residues of the oligosaccharide occupy the primary binding site. The middle mannose residues have marginally higher preference over the non-reducing end residue. The sugar binding site of ConA is extended and accommodates at least three alpha(1-2) linked mannose residues. Based on the present calculations two mechanisms have been proposed for the binding of alpha(1-2) linked mannotriose and tetraose to ConA.

Mismatch repair genes of eukaryotes

Mismatches that arise during replication or genetic recombination or owing to damage to DNA by chemical agents are recognized by mismatch repair systems. The pathway has been characterized in detail in Escherichia coli. Several homologues of the genes encoding the proteins of this pathway have been identified in the yeast Saccharomyces cerevisiae and in human cells. Mutations in the human genes hMSH2, hMLH1, hPMS1 and hPMS2 have been linked to hereditary nonpolyposis colon cancer (HNPCC) and to some sporadic tumours. Mismatch repair also plays an antirecombinogenic role and is implicated in speciation.

Reactions of cyanogen radical with alkanes and an explanation for negative temperature dependence of rate constants

Reactions of cyanide radicals with alkanes have been investigated by ab initio methods. It is found that the potential energy surface for reaction of CN with a primary C-H bond in methane has a small positive barrier while reactions of CN with a secondary and a tertiary C-H bond in alkanes are barrierless at the correlated level. A simple explanation for the obtained negative temperature dependence of rate constants for reactions of CN with a secondary and a tertiary C-H bond in alkanes are given in terms of the collision theory of bimolecular reactions. It is shown that for barrierless reactions the negative temperature dependence of the rate constants is attributed to the variation of the pre-exponential factor with temperature.

New records from India and redescripton of Corynascus thermophilus and its anamorph Myceliophthora fergusii

Studies of Indian thermophilic fungi have yielded several isolations of Myceliophthora fergusii, anamorph of the heterothallic ascomycete Corynascus thermophilus (Thielaviaceae). Identification was confirmed by matings. Chrysosporium fermentotritici is a synonym of M. fergusii.

Mathematical modelling of divided blast cupola

A pseudo 2-D mathematical model has been developed to simulate a cupola with one row and two rows of tuyere. The simulation results predicted higher spout temperature and combustion ratio for cupola with two rows of tuyere compared to that with one row. Further, the model has been used to study the effect of the distance of separation between the two rows of tuyere on cupola performance. The computed results shows that the spout temperature increases with tuyere level separation and attains the maximum at an optimum distance of separation between two rows of tuyere. Above the optimum, the spout temperature starts decreasing. The exit gas temperature and combustion ratio increases monotonously with the increase in tuyere level separation. These results agree well with the reported experimental observations. The mechanism behind the improved cupola performance with two rows of tuyere has been deduced from the computed temperature and composition profiles inside the cupola.

Passive pressure coefficients, critical failure surface and its kinematic admissibility

Using a combination of a logarithmic spiral and a straight line as a failure surface, comprehensive charts have been developed to determine the passive earth pressure coefficients and the positions of the critical failure surface for positive as well as negative wall friction angles. Translational movement of the wall has been examined in detail, considering the soil as either an associated flow dilatant material or a non-dilatant material, to determine the kinematic admissibility of the limit equilibrium solutions.

Reactivation kinetics of boron acceptors in hydrogenated silicon during zero bias anneal

The reactivation kinetics of passivated boron accepters in hydrogenated silicon during zero bias annealing in the temperature range of 65-130 degrees C are reported, For large annealing times and high annealing temperatures, the reactivation process follows second-order kinetics and is rate limited by a thermally activated <(H)over tilde (2)> complex formation process, For short annealing times and low annealing temperatures, the reactivation rate is found to be larger than that due to <(H)over tilde (2)> complex formation alone. We conclude that the faster reactivation is caused by the diffusion of the liberated hydrogen atoms into the bulk as well as <(H)over tilde (2)> complex formation. The effective diffusion coefficient of hydrogen is measured and found to obey the Arrhenius relation with an activation energy (1.41 +/- 0.1) eV. (C) 1997 American Institute of Physics.

Risk-sensitive optimal control for Markov decision processes with monotone cost

The existence of an optimal feedback law is established for the risk-sensitive optimal control problem with denumerable state space. The main assumptions imposed are irreducibility and a near monotonicity condition on the one-step cost function. A solution can be found constructively using either value iteration or policy iteration under suitable conditions on initial feedback law.