Design of a Near Optimum Regulator for a Power Plant

For systems which can be decomposed into slow and fast subsystems, a near optimum linear state regulator consisting of two subsystem regulators can be developed. Depending upon the desired criteria, either a short term (fast controller) or a long term controller (slow controller) can be easily designed with minimum computational costs. Using this approach an example of a power system supplying a cyclic load is studied and the performance of the different controllers are compared.

Characterization of protoporphyrin as the physiological regulator of delta-aminolevulinate dehydratase in Neurospora crassa

In Neurospora crassa, the activity of δ-aminolevulinate dehydratase, the second and rate-limiting enzyme of the heme-biosynthetic pathway, is low in normal cells compared to the activity detected in plants, animals and bacteria. The activity is almost undetectable when Neurospora crassa is grown under iron-deficient conditions. The enzyme activity increases strikingly on addition of iron to iron-deficient cultures. This increase can be blocked by the addition of protoporphyrin, the penultimate product of the heme-biosynthetic pathway, to the cultures. The question whether iron directly acts at the genetic level or acts merely by removing protoporphyrin, converting the latter into heme prosthetic groups of hemoproteins, has been investigated by studying the effect of inhibition of heme synthesis on the induction of δ-aminolevulinate dehydratase. It has been found that treatments with levulinic acid or cyanide which inhibit the formation of the porphyrin moiety, induce δ-aminolevulinate dehydratase, whereas treatments which inhibit at a step after protoporphyrin formation (iron-deficiency and cobalt treatment) repress the enzyme. The endogenous levels of protoporphyrin are strictly controlled: a decrease below the optimum level causing induction and an increase above the optimum level leading to repression of δ-aminolevulinate dehydratase. Levulinic acid and cyanide can induce the enzyme in iron-deficient cultures in the absence of added iron, indicating that the metal iron acts only by converting protoporphyrin to heme fixed in hemoproteins in Neurospora crassa. Therefore it is suggested that protoporphyrin is the physiological regulator of δ-aminolevulinate dehydratase in Neurospora crassa.

Identification of key DNA elements involved in promoter recognition by Mxr1p, a master regulator of methanol utilization pathway in Pichia pastoris

Mxr1p (methanol expression regulator 1) functions as a key regulator of methanol metabolism in the methylotrophic yeast Pichia pastoris. In this study, a recombinant Mxr1p protein containing the N-terminal zinc finger DNA binding domain was overexpressed and purified from E coli cells and its ability to bind to promoter sequences of AOXI encoding alcohol oxidase was examined. In the AOXI promoter, Mxr1p binds at six different regions. Deletions encompassing these regions result in a significant decrease in AOXI promoter activity in vivo. Based on the analysis of AOXI promoter sequences, a consensus sequence for Mxr1p binding consisting of a core 5' CYCC 3' motif was identified. When the core CYCC sequence is mutated to CYCA, CYCT or CYCM (M = 5-methylcytosine), Mxr1p binding is abolished. Though Mxr1p is the homologue of Saccharomyces cerevisiae Adr1p transcription factor, it does not bind to Adr1p binding site of S. cerevisiae alcohol dehydrogenase promoter (ADH2UAS1). However, two point mutations convert ADH2UAS1 into an Mxr1p binding site. The identification of key DNA elements involved in promoter recognition by Mxr1p is an important step in understanding its function as a master regulator of the methanol utilization pathway in P. pastoris.

Trishanku, a novel regulator of cell-type stability and morphogenesis in Dictyostelium discoideum

We have identified a novel gene, trishanku (triA), by random insertional mutagenesis of Dictyostelium discoideum. TriA is a Broad complex Tramtrack bric-a-brac domain-containing protein that is expressed strongly during the late G2 phase of cell cycle and in presumptive spore (prespore (psp)) cells. Disrupting triA destabilizes cell fate and reduces aggregate size; the fruiting body has a thick stalk, a lowered spore: stalk ratio, a sub-terminal spore mass and small, rounded spores. These changes revert when the wild-type triA gene is re-expressed under a constitutive or a psp-specific promoter. By using short- and long-lived reporter proteins, we show that in triA(-) slugs the prestalk (pst)/psp proportion is normal, but that there is inappropriate transdifferentiation between the two cell types. During culmination, regardless of their current fate, all cells with a history of pst gene expression contribute to the stalk, which could account for the altered cell-type proportion in the mutant.

Role of a PAS sensor domain in the Mycobacterium tuberculosis transcription regulator Rv1364c

The Mycobacterium tuberculosis transcriptional regulator Rv1364c regulates the activity of the stress response sigma factor sigma(F). This multi-domain protein has several components: a signaling PAS domain and an effector segment comprising of a phosphatase, a kinase and an anti-anti-sigma factor domain. Based on Small Angle X-ray Scattering (SAXS) data, Rv1364c was recently shown to be a homo-dimer and adopt an elongated conformation in solution. The PAS domain could not be modeled into the structural envelope due to poor sequence similarity with known PAS proteins. The crystal structure of the PAS domain described here provides a structural basis for the dimerization of Rv1364c. It thus appears likely that the PAS domain regulates the anti-sigma activity of Rv1364c by oligomerization. A structural comparison with other characterized PAS domains reveal several sequence and conformational features that could facilitate ligand binding - a feature which suggests that the function of Rv1364c could potentially be governed by specific cellular signals or metabolic cues. (C) 2010 Elsevier Inc. All rights reserved.

Heme is a positive regulator of cytochrome P-450 gene transcription

Inhibitors of heme biosynthesis such as CoCl2, 3-amino-1,2,4-triazole, and thioacetamide block the 3-methylcholanthrene-mediated induction of cytochrome P-450 (c + d) messenger RNAs and their transcription in rat liver. This effect is specific, since the messenger RNA levels for albumin and glutathione transferase (Ya + Yc) and their transcription are not significantly influenced under conditions of heme depletion. Exogenous administration of heme at very low doses (50 μg/100 g body wt) is able to completely counteract the effects of the heme biosynthetic inhibitors on cytochrome P-450 (c + d) messenger RNA levels and their transcription. This constitutes a direct proof for the role of heme as a positive regulator of cytochrome P-450 gene transcription.

Integration-free algorithms for fixed end-point regulator problems

A new formulation is suggested for the fixed end-point regulator problem, which, in conjunction with the recently developed integration-free algorithms, provides an efficient means of obtaining numerical solutions to such problems.

A Nonlinear Voltage Regulator With One Tunable Parameter for Multimachine Power Systems

This paper proposes a nonlinear voltage regulator with one tunable parameter for multimachine power systems. Based on output feedback linearization, this regulator can achieve simultaneous voltage regulation and small-signal performance objectives. Conventionally output feedback linearization has been used for voltage regulator design by taking infinite bus voltage as reference. Unfortunately, this controller has poor small-signal performance and cannot be applied to multimachine systems without the estimation of the equivalent external reactance seen from the generator. This paper proposes a voltage regulator design by redefining the rotor angle at each generator with respect to the secondary voltage of the step-up transformer as reference instead of a common synchronously rotating reference frame. Using synchronizing and damping torques analysis, we show that the proposed voltage regulator achieves simultaneous voltage regulation and damping performance over a range of system and operating conditions by controlling the relative angle between the generator internal voltage angle delta and the secondary voltage of the step up transformer. The performance of the proposed voltage regulator is evaluated on a single machine infinite bus system and two widely used multimachine test systems.

Continuous-time Single Network Adaptive Critic for Regulator Design of Nonlinear Control Affine Systems

An optimal control law for a general nonlinear system can be obtained by solving Hamilton-Jacobi-Bellman equation. However, it is difficult to obtain an analytical solution of this equation even for a moderately complex system. In this paper, we propose a continuoustime single network adaptive critic scheme for nonlinear control affine systems where the optimal cost-to-go function is approximated using a parametric positive semi-definite function. Unlike earlier approaches, a continuous-time weight update law is derived from the HJB equation. The stability of the system is analysed during the evolution of weights using Lyapunov theory. The effectiveness of the scheme is demonstrated through simulation examples.

Scattering theory and linear optimal control: Regulator and servo problems

In this paper, several known computational solutions are readily obtained in a very natural way for the linear regulator, fixed end-point and servo-mechanism problems using a certain frame-work from scattering theory. The relationships between the solutions to the linear regulator problem with different terminal costs and the interplay between the forward and backward equations have enabled a concise derivation of the partitioned equations, the forward-backward equations, and Chandrasekhar equations for the problem. These methods have been extended to the fixed end-point, servo, and tracking problems.

Damping and synchronising torques contributed by a voltage regulator to a synchronous generator: a quantitative assessment

In the paper, the total damping and synchronising torques, which determine the dynamic stability of a synchronous generator in a power system, have been traced to their origin. The positive and negative components released or consumed by the voltage regulator, and by the various windings of the machine, have been isolated, with the object of making a quantitative assessment of the effects of various gains and time constants on the dynamic stability of a synchronous machine under different operating conditions. The analysis is based on the properties of quadratic invariance in tensor calculus. An alternative solution by network analysis has also been provided to establish the validity of the tensor approach.

Serine/Threonine/Tyrosine Protein Kinase Phosphorylates Oleosin, a Regulator of Lipid Metabolic Functions

Plant oils are stored in oleosomes or oil bodies, which are surrounded by a monolayer of phospholipids embedded with oleosin proteins that stabilize the structure. Recently, a structural protein, Oleosin3 (OLE3), was shown to exhibit both monoacylglycerol acyltransferase and phospholipase A(2) activities. The regulation of these distinct dual activities in a single protein is unclear. Here, we report that a serine/threonine/tyrosine protein kinase phosphorylates oleosin. Using bimolecular fluorescence complementation analysis, we demonstrate that this kinase interacts with OLE3 and that the fluorescence was associated with chloroplasts. Oleosin-green fluorescent protein fusion protein was exclusively associated with the chloroplasts. Phosphorylated OLE3 exhibited reduced monoacylglycerol acyltransferase and increased phospholipase A(2) activities. Moreover, phosphatidylcholine and diacylglycerol activated oleosin phosphorylation, whereas lysophosphatidylcholine, oleic acid, and Ca2+ inhibited phosphorylation. In addition, recombinant peanut (Arachis hypogaea) kinase was determined to predominantly phosphorylate serine residues, specifically serine-18 in OLE3. Phosphorylation levels of OLE3 during seed germination were determined to be higher than in developing peanut seeds. These findings provide direct evidence for the in vivo substrate selectivity of the dual-specificity kinase and demonstrate that the bifunctional activities of oleosin are regulated by phosphorylation.

Involvement of the Global Regulator H-NS in the Survival of Escherichia coli in Stationary Phase

Long-term batch cultures of Escherichia coli grown in nutrient-rich medium accumulate mutations that provide a growth advantage in the stationary phase (GASP). We have examined the survivors of prolonged stationary phase to identify loci involved in conferring a growth advantage and show that a mutation in the hns gene causing reduced activity of the global regulator H-NS confers a GASP phenotype under specific conditions. The hns-66 allele bears a point mutation within the termination codon of the H-NS open reading frame, resulting in a longer protein that is partially functional. Although isolated from a long-term stationary-phase culture of the parent carrying the rpoS819 allele that results in reduced RpoS activity, the hns-66 survivor showed a growth disadvantage in the early stationary phase (24 to 48 h) when competed against the parent. The hns-66 mutant is also unstable and reverts at a high frequency in the early stationary phase by accumulating second-site suppressor mutations within the ssrA gene involved in targeting aberrant proteins for proteolysis. The mutant was more stable and showed a moderate growth advantage in combination with the rpoS819 allele when competed against a 21-day-old parent. These studies show that H-NS is a target for mutations conferring fitness gain that depends on the genetic background as well as on the stage of the stationary phase.

Under-representation of intrinsic terminators across bacterial genomic islands: Rho as a principal regulator of xenogenic DNA expression

Two transcription termination mechanisms - intrinsic and Rho-dependent - have evolved in bacteria. The Rho factor occurs in most bacterial lineages, and has been hypothesized to play a global regulatory role. Genome-wide studies using microarray, 2D-gel electrophoresis and ChIP-chip provided evidence that Rho serves to silence transcription from horizontally acquired genes and prophages in Escherichia coli K-12, implicating the factor to be a part of the ``cellular immune mechanism'' protecting against deleterious phages and aberrant gene expression from acquired xenogenic DNA. We have investigated this model by adopting an alternate in silico approach and have extended the study to other species. Our analysis shows that several genomic islands across diverse phyla have under-representation of intrinsic terminators, similar to that experimentally observed in E. coli K-12. This implies that Rho-dependent termination is the predominant process operational in these islands and that silencing of foreign DNA is a conserved function of Rho. From the present analysis, it is evident that horizontally acquired islands have lost intrinsic terminators to facilitate Rho-dependent termination. These results underscore the importance of Rho as a conserved, genome-wide sentinel that regulates potentially toxic xenogenic DNA. (C) 2012 Elsevier B.V. All rights reserved.