Analysis of the beta-glucoside utilization (bgl) genes of Shigella sonnei: evolutionary implications for their maintenance in a cryptic state

The pattern of expression of the genes involved in the utilization of aryl beta-glucosides such as arbutin and salicin is different in the genus Shigella compared to Escherichia coli. The results presented here indicate that the homologue of the cryptic bgl operon of E. coli is conserved in Shigella sonnei and is the primary system involved in beta-glucoside utilization in the organism. The organization of the bgl genes in 5. sonnei is similar to that of E. coli; however there are three major differences in terms of their pattern of expression. (i) The bglB gene, encoding phospho-beta-glucosidase B, is insertionally inactivated in 5. sonnei. As a result, mutational activation of the silent bgl promoter confers an Arbutin-positive (Arb(+)) phenotype to the cells in a single step; however, acquiring a Salicin-positive (Sal(+)) phenotype requires the reversion or suppression of the bglB mutation in addition. (ii) Unlike in E. coli, a majority of the activating mutations (conferring the Arb(+) phenotype) map within the unlinked hns locus, whereas activation of the E. coli bgl operon under the same conditions is predominantly due to insertions within the bglR locus. (iii) Although the bgl promoter is silent in the wild-type strain of 5. sonnei (as in the case of E. coli), transcriptional and functional analyses indicated a higher basal level of transcription of the downstream genes. This was correlated with a 1 bp deletion within the putative Rho-independent terminator present in the leader sequence preceding the homologue of the bglG gene. The possible evolutionary implications of these differences for the maintenance of the genes in the cryptic state are discussed.

Air-fleet and maintenance facility planning

This paper describes the use of simulation in the planning and operation of a small fleet of aircraft typical of the air force of a developing country. We consider a single flying base, where the opera tionally ready aircraft are stationed, and a repair depot, where the planes are overhauled. The measure of effectiveness used is "system availability, the percentage of airplanes that are usable. The system is modeled in GPSS as a cyclic queue process. The simulation model is used to perform sensitivity analyses and to validate the principal assumptions of the analytical model on which the simulation model is based.

Systems analysis for planning of air fleets and maintenance facilities

The high cost and extraordinary demands made on sophisticated air defence systems, pose hard challenges to the managers and engineers who plan the operation and maintenance of such systems. This paper presents a study aimed at developing simulation and systems analysis techniques for the effective planning and efficient operation of small fleets of aircraft, typical of the air force of a developing country. We consider an important aspect of fleet management: the problem of resource allocation for achieving prescribed operational effectiveness of the fleet. At this stage, we consider a single flying-base, where the operationally ready aircraft are stationed, and a repair-depot, where the planes are overhauled. An important measure of operational effectiveness is ‘ availability ’, which may be defined as the expected fraction of the fleet fit for use at a given instant. The tour of aircraft in a flying-base, repair-depot system through a cycle of ‘ operationally ready ’ and ‘ scheduled overhaul ’ phases is represented first by a deterministic flow process and then by a cyclic queuing process. Initially the steady-state availability at the flying-base is computed under the assumptions of Poisson arrivals, exponential service times and an equivalent singleserver repair-depot. This analysis also brings out the effect of fleet size on availability. It defines a ‘ small ’ fleet essentially in terms of the important ‘ traffic ’ parameter of service rate/maximum arrival rate.A simulation model of the system has been developed using GPSS to study sensitivity to distributional assumptions, to validate the principal assumptions of the analytical model such as the single-server assumption and to obtain confidence intervals for the statistical parameters of interest.

Autoimmune Regulator (AIRE) in the Maintenance of Immunological Tolerance

Autoimmune regulator (AIRE) is the gene mutated in the human polyglandular autoimmune disease called Autoimmune polyendocrinopathy, candidiasis, and ectodermal dystrophy (APECED) that belongs to the Finnish disease heritage. Murine Aire has been shown to be important in the generation of the T cell central tolerance in the thymus by promoting the expression of ectopic tissue-specific antigens in the thymic medulla. Aire is also involved in the thymus tissue organization during organogenesis. In addition to the thymus, AIRE/Aire is expressed in the secondary lymphoid organs. Accordingly, a role for AIRE/Aire in the maintenance of peripheral tolerance has been suggested. Peripheral tolerance involves mechanisms that suppress immune responses in secondary lymphoid organs. Regulatory T cells (Tregs) are an important suppressive T cell population mediating the peripheral tolerance. Tregs are generated in the thymus but also in the peripheral immune system T cells can acquire the Treg-phenotype. The aim of this study was to characterize Tregs in APECED patients and in the APECED mouse model (Aire-deficient mice). In the mouse model, it was possible to separate Aire expression in the thymus and in the secondary lymphoid organs. The relative importance of thymic and peripheral Aire expression in the maintenance of immunological tolerance was studied in an experimental model that was strongly biased towards autoimmunity, i.e. lymphopenia-induced proliferation (LIP) of lymphocytes. This experimental model was also utilised to study the behaviour of T cells with dual-specific T cell receptors (TCR) during the proliferation. The Treg phenotype was studied by flow cytometry and relative gene expression with real-time polymerase chain reaction. TCR repertoires of the Tregs isolated from APECED patients and healthy controls were also compared. The dual-specific TCRs were studied with the TCR repertoire analysis that was followed with sequencing of the chosen TCR genes in order to estimate changes in the dual-specific TCR diversity. The Treg function was tested with an in vitro suppression assay. The APECED patients had normal numbers of Tregs but the phenotype and suppressive functions of the Tregs were impaired. In order to separate Aire functions in the thymus from its yet unknown role in the secondary lymphoid organs, the phenomenon of LIP was utilised. In this setting, the lymphocytes that are adoptively transferred to a lymphopenic recipient proliferate to stimuli from self-originating antigens. This proliferation can result in autoimmunity if peripheral tolerance is not fully functional. When lymphocytes that had matured without Aire in the thymus were transferred to lymphopenic Aire-sufficient recipients, no clinical autoimmunity followed. The Aire-deficient donor-originating lymphocytes hyperproliferated, and other signs of immune dysregulation were also found in the recipients. Overt autoimmunity, however, was prevented by the Aire-deficient donor-originating Tregs that hyperproliferated in the recipients. Aire-deficient lymphopenic mice were used to study whether peripheral loss of Aire had an impact on the maintenance of peripheral tolerance. When normal lymphocytes were transferred to these Aire-deficient lymphopenic recipients, the majority of recipients developed a clinically symptomatic colitis. The colitis was confirmed also by histological analysis of the colon tissue sections. In the Aire-deficient lymphopenic recipients Tregs were proliferating significantly less than in the control group s recipients that had normal Aire expression in their secondary lymphoid organs. This study shows that Aire is not only important in the central tolerance but is also has a significant role in the maintenance of the peripheral tolerance both in mice and men. Aire expressed in the secondary lymphoid organs is involved in the functions of Tregs during an immune response. This peripheral expression appears to be relatively more important in some situations since only those lymphopenic recipients that had lost peripheral expression of Aire developed a symptomatic autoimmune disease. This AIRE-related Treg defect could be clinically important in understanding the pathogenesis of APECED.

Small Ubiquitin-related Modifier Ligase Activity of Mms21 Is Required for Maintenance of Chromosome Integrity during the Unperturbed Mitotic Cell Division Cycle in Saccharomyces cerevisiae

The SUMO ligase activity of Mms21/Nse2, a conserved member of the Smc5/6 complex, is required for resisting extrinsically induced genotoxic stress. We report that the Mms21 SUMO ligase activity is also required during the unchallenged mitotic cell cycle in Saccharomyces cerevisiae. SUMO ligase-defective cells were slow growing and spontaneously incurred DNA damage. These cells required caffeine-sensitive Mec1 kinase-dependent checkpoint signaling for survival even in the absence of extrinsically induced genotoxic stress. SUMO ligase-defective cells were sensitive to replication stress and displayed synthetic growth defects with DNA damage checkpoint-defective mutants such as mec1, rad9, and rad24. MMS21 SUMO ligase and mediator of replication checkpoint 1 gene (MRC1) were epistatic with respect to hydroxyurea-induced replication stress or methyl methanesulfonate-induced DNA damage sensitivity. Subjecting Mms21 SUMO ligase-deficient cells to transient replication stress resulted in enhancement of cell cycle progression defects such as mitotic delay and accumulation of hyperploid cells. Consistent with the spontaneous activation of the DNA damage checkpoint pathway observed in the Mms21-mediated sumoylation-deficient cells, enhanced frequency of chromosome breakage and loss was detected in these mutant cells. A mutation in the conserved cysteine 221 that is engaged in coordination of the zinc ion in Loop 2 of the Mms21 SPL-RING E3 ligase catalytic domain resulted in strong replication stress sensitivity and also conferred slow growth and Mec1 dependence to unchallenged mitotically dividing cells. Our findings establish Mms21-mediated sumoylation as a determinant of cell cycle progression and maintenance of chromosome integrity during the unperturbed mitotic cell division cycle in budding yeast.

Recommendations for driver licensing and traffic law enforcement in India aiming to improve road safety

During the last decade, developing countries such as India have been exhibiting rapid increase in human population and vehicles, and increase in road accidents. Inappropriate driving behaviour is considered one of the major causes of road accidents in India as compared to defective geometric design of pavement or mechanical defects in vehicles. It can result in conditions such as lack of lane discipline, disregard to traffic laws, frequent traffic violations, increase in crashes due to self-centred driving, etc. It also demotivates educated drivers from following good driving practices. Hence, improved driver behaviour can be an effective countermeasure to reduce the vulnerability of road users and inhibit crash risks. This article highlights improved driver behaviour through better driver education, driver training and licensing procedures along with good on-road enforcement; as an effective countermeasure to ensure road safety in India. Based on the review and analysis, the article also recommends certain measures pertaining to driver licensing and traffic law enforcement in India aimed at improving road safety.

Incentive compatible mechanisms for group ticket allocation in software maintenance services

A customer reported problem (or Trouble Ticket) in software maintenance is typically solved by one or more maintenance engineers. The decision of allocating the ticket to one or more engineers is generally taken by the lead, based on customer delivery deadlines and a guided complexity assessment from each maintenance engineer. The key challenge in such a scenario is two folds, un-truthful (hiked up) elicitation of ticket complexity by each engineer to the lead and the decision of allocating the ticket to a group of engineers who will solve the ticket with in customer deadline. The decision of allocation should ensure Individual and Coalitional Rationality along with Coalitional Stability. In this paper we use game theory to examine the issue of truthful elicitation of ticket complexities by engineers for solving ticket as a group given a specific customer delivery deadline. We formulate this problem as strategic form game and propose two mechanisms, (1) Division of Labor (DOL) and (2) Extended Second Price (ESP). In the proposed mechanisms we show that truth telling by each engineer constitutes a Dominant Strategy Nash Equilibrium of the underlying game. Also we analyze the existence of Individual Rationality (IR) and Coalitional Rationality (CR) properties to motivate voluntary and group participation. We use Core, solution concept from co-operative game theory to analyze the stability of the proposed group based on the allocation and payments.