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mexCD - oprJ is an envelope stress-inducible multidrug efflux operon of P seudomonas aeruginosa. A gene encoding a homologue of the NfxB repressor of this operon, PA4596, occurs downstream of oprJ and was proposed as a second repressor of this efflux operon. Inactivation of this gene had no impact on mexCD - oprJ expression in cells not exposed to envelope stress although its loss under envelope stress conditions yielded a > 10-fold increase in mexCD - oprJ expression. Consistent with PA4596 functioning as a mexCD - oprJ repressor, the purified protein was able to bind to a DNA fragment carrying the mexCD - oprJ promoter region. Expression of PA4596 was induced under conditions of envelope stress dependent on the AlgU envelope stress sigma factor, consistent with PA4596 operating under envelope stress conditions where it possibly serves to moderate envelope stress-inducible mexCD - oprJ expression. nfxB mutants showed elevated PA4596 expression and purified NfxB bound to DNA encompassing the PA4596 upstream region, an indication that NfxB functions as a repressor of PA4596 expression. Elimination of PA4596 in P . aeruginosa lacking nfxB and hyperexpressing mexCD - oprJ had no additional impact on mexCD - oprJ expression, regardless of the presence of envelope stress, suggesting that PA4596 repressor activity may be dependent on NfxB. This envelope stress-regulated repressor of mexCD - oprJ has been renamed esrC. [ABSTRACT FROM AUTHOR]

Empirical models of spatial voting allow us to infer legislators' locations in an abstract policy or ideological space using their roll-call votes. Over the past 25 years, these models have provided new insights about the U.S. Congress, and legislative behavior more generally. There are now a number of alternative models, estimators, and software packages that researchers can use to recover latent issue or ideological spaces from voting data. These different tools usually produce substantively similar estimates, but important differences also arise. We investigated the sources of observed differences between two leading methods, NOMINATE and IDEAL. Using data from the 1994 to 1997 Supreme Court and the 109th Senate, we determined that while some observed differences in the estimates produced by each model stem from fundamental differences in the models' underlying behavioral assumptions, others arise from arbitrary differences in implementation. Our Monte Carlo experiments revealed that neither model has a clear advantage over the other in the recovery of legislator locations or roll-call midpoints in either large or small legislatures. [ABSTRACT FROM AUTHOR]

Both pundits and scholars have blamed increasing levels of partisan conflict and polarization in Congress on the effects of partisan gerrymandering. We assess whether there is a strong causal relationship between congressional districting and polarization. We find very little evidence for such a link. First, we show that congressional polarization is primarily a function of the differences in how Democrats and Republicans represent the same districts rather than a function of which districts each party represents or the distribution of constituency preferences. Second, we conduct simulations to gauge the level of polarization under various “neutral” districting procedures. We find that the actual levels of polarization are not much higher than those produced by the simulations. We do find that gerrymandering has increased the Republican seat share in the House; however, this increase is not an important source of polarization. [ABSTRACT FROM AUTHOR]

The article discusses the roll-call voting behavior of House and Senate members changing party affiliation during the course of their political careers. The behavioral consequences of party defections across the three two-party systems to learn how important differences in the political environment may have exerted different influences on the behavior of party switchers. The overall patterns of roll-call voting differ substantially across the three two-party systems. The assessment of the effect of party switches on voting behavior involves identifying those individuals who changed party affiliation at some time during their congressional careers.

MexAB-OprM is a multidrug efflux system that contributes to intrinsic and acquired multidrug resistance in Pseudomonas aeruginosa, the latter as a result of mutational hyperexpression of the mexAB-oprM operon. While efflux gene hyperexpression typically results from mutations in the linked mexR repressor gene, it also occurs independently of mexR mutations in so-called nalC mutants that demonstrate more modest mexAB-oprM expression and, thus, more modest multidrug resistance than do mexR strains. Using a transposon insertion mutagenesis approach, nalC mutant strains were selected and the disrupted gene, PA3721, identified. Amplification and sequencing of this gene from previously isolated spontaneous nalC mutants revealed the presence of mutations in all instances and as such, PA3721 has been renamed nalC. PA3721 ( nalC) encodes a probable repressor of the TetR/AcrR family and occurs upstream of an apparent two-gene operon, PA3720–PA3719, whose expression was negatively regulated by PA3721. Thus, PA3720-PA3719 was hyperexpressed in transposon insertion and spontaneous nalC mutants. The loss of PA3719 but not of PA3720 expression in a spontaneous nalC mutant reduced MexAB-OprM expression to wild-type levels and compromised multidrug resistance, an indication that hyperexpression of PA3719 only was necessary for the nalC phenotype. Introduction of PA3719 into wild-type P. aeruginosa on a multicopy plasmid was, in fact, sufficient to promote elevated MexAB-OprM expression and multidrug resistance characteristic of a nalC strain. Thus, the nalC (PA3721) mutation serves only to enhance PA3720-PA3719 expression, with expression of PA3719 (encodes a 53 amino acid protein of predicted pI 10.4) directly or indirectly impacting MexAB-OprM expression. Intriguingly, nalC strains produce markedly elevated levels of stable MexR protein suggesting that PA3720-PA3719 hyperexpression somehow modulates MexR repressor activity. The deduced products of PA3720-PA3719 show no homology to sequences presently in the GenBank databases, however, and as such provide no clues as to how this might occur. [ABSTRACT FROM AUTHOR]

Proposes an estimator of variation in party influence in roll-call voting in the United States Congress. Use of a spatial model; Consistency between the Rice index of party dissimilarity and a 'party-less' null model; Changes associated with the packing of the Rules Committee in 1961 and the procedural reforms of 1973.

Under iron limitation, Pseudomonas aeruginosa secretes a fluorescent siderophore called pyoverdin, which, after complexing iron, is transported back into the cell via its outer membrane receptor FpvA. Previous studies demonstrated co-purification of FpvA with iron-free PaA and reported similar binding affinities of iron-free pyoverdin and ferric-pyoverdin to purified FpvA. The fluorescence resonance energy transfer between iron-free PaA and the FpvA receptor here reveals the existence of an FpvA–pyoverdin complex in P. aeruginosa in vivo, suggesting that the pyoverdin-loaded FpvA is the normal state of the receptor in the absence of iron. Using tritiated ferric-pyoverdin, it is shown that iron-free PaA binds to the outer membrane but is not taken up into the cell, and that in vitro and, presumably, in vivo ferric-pyoverdin displaces the bound iron-free pyoverdin on FpvA–PaA to form FpvA–PaA-Fe complexes. In vivo, the kinetics of formation of this FpvA–PaA-Fe complex are more than two orders of magnitude faster than in vitro and depend on the presence of TonB. In P. aeruginosa, two tonB genes have been identified (tonB1 and tonB2). TonB1 is directly involved in ferric-pyoverdin uptake, and TonB2 seems to be able partially to replace TonB1 in its role in iron acquisition. However, no effect of TonB1 or TonB2 on the apparent affinity of free pyoverdin to FpvA was observed, and a 17-fold difference was measured between the affinities of the two forms of pyoverdin (PaA and PaA-Fe) to FpvA in the absence of TonB1 or TonB2. The mechanism of iron uptake in P. aeruginosa via the pyoverdin pathway is discussed in view of these new findings. [ABSTRACT FROM AUTHOR]

A binding protein for inorganic phosphate was purified to apparent homogeneity from the shock fluids of phosphate-limited Pseudomonas aeruginosa. The purified protein bound one molecule of phosphate per molecule of binding protein with an average Kd of 0.34 μM. Arsenate, pyrophosphate and polyphosphates up to 15 units long could inhibit the binding of phosphate to the binding protein, although organic phosphates, such as glucose 6-phosphate, glycerol 3-phosphate and adenosine 5′-monophosphate could not. Mutants lacking the phosphate- binding protein were isolated and shown to be deficient in phosphate transport compared with wild-type cells. Two kinetically distinct systems for phosphate uptake could be observed in wild-type cells, with apparent Km values of 0.46 ± 0.10 μM (high affinity) and 12.0 ± 1.6 μM (low affinity). In contrast, only a single low-affinity transport system was observable in mutants lucking the binding protein (Km apparent = 19.3 ± 1.4 μM Pi), suggesting the involvement of the binding protein in the inducible high-affinity phosphate-uptake system of P. aeruginosa. [ABSTRACT FROM AUTHOR]

Develops a scaling procedure for estimating the latent/unobservable dimensions underlying a set of manifest/observable variables. Analysis of the data matrix directly; Details on the scaling procedure and its use; Discussion of a number of applications to political data.

Examines the relationship between voter information, voter preference and electoral choice in the United States. Measurement of the level of voter information using the Aldrich-McKelvey scaling procedure; Conditional logit analysis of the effect of information on turnout and vote choice; Analysis of the effect of voter information levels on classification accuracy.

Proposes the use of a general nonlinear logit model in analyzing the political choices of voters in the United States. Assumptions for probabilistic voting based on a spatial utility function; Parameters of the utility function and the spatial coordinates of the choices; Robustness and face validity of the model.

Presents a methodology for the empirical estimation of spatial voting models in elections in the United States from 1968 to 1980. Parameters of the utility functions; Hypothesis of sincere and spatial voting in two-candidate elections; Factors behind the low turnout of voters during elections.

Examines the dimensionality of interest group ratings of senators in the United States, from 1969-1978. Use of unfolding analysis to determine the structure of preferential choice; Correlation between the actual interest group ratings and the ratings predicted by the unfolding method; Analysis of the senator's behavior; Differences for the reelected and defeated senators.

OprJ, overproduced in nfxBmultidrug-resistant strains of Pseudomonas aeruginosa, and OprK, overproduced in the multidrug-resistant strain K385, were demonstrated to be immunologically cross-reactive using an OprJ-specific monoclonal antibody. Treatment of the purified proteins with trypsin or chymotrypsin yielded virtually Indistinguishable digestion patterns, and the N-terminal sequence of two trypsin fragments was identical for both proteins, indicating that OprJ and OprK share identity. The N-terminal amino acid sequences were used to facilitate cloning of the oprJ gene on a 5 kbp KpnI fragment and a 10 kbp BamHI fragment. Nucleotide sequencing of portions of these fragments revealed that oprJ was the terminal gene in a putative three-gene operon, mexC--mexD--oprJ. The predicted mexC--mexD--oprJ gene products exhibit homology to the MexA--MexB--OprM components of the multidrug-resistance efflux pump of P. aeruginosa (43-46% identity). Consistent with an implied role for mexC--mexD--oprJ in drug efflux, the mexC--mexD--oprJ-hyperexpressing strain K385 showed reduced accumulation of a variety of antibiotics as compared with its parent strain, and this drug 'exclusion' was abrogated by energy inhibitors. The mexC and oprJ products are putative lipoproteins of a molecular mass of 40707 and 51 742 Da, respectively, while mexD was predicted to encode a protein of 111 936 Da. Sequencing upstream of mexC revealed the presence of the nfxB gene transcribed divergently from the effiux genes. Overproduction of OprJ and the attendant multiple-antibiotic resistance of strain K385 was shown to result from a point mutation in nfxB, resulting in a H87→R change in the predicted NfxB polypeptide. OprJ overproduction and multidrug resistance in K385 was reversed by the cloned nfxB gene, suggesting that nfxB encodes a repressor of mexC--mexD--oprJ expression. Consistent with this, the cloned nfxB gene repressed synthesis of a mexC--lacZ fusion in Escherichia coli. nfxB also repressed expression of a nfxB--lacZ fusion, indicating that NfxB negatively regulates its own expression. These data indicate that the multidrug resistance of nfxB strains is due to overexpression of an efflux operon, mexC--mexD--oprJ, encoding components of a second efflux pump in P. aeruginosa. [ABSTRACT FROM AUTHOR]

Pseudomonas aeruginosa strain K437 is defective in the production of a 90 kDa ferripyoverdine receptor and is unable to grow in an iron-deficient medium in the presence of the non-metabolizable iron chelator 2,2′-dipyridyl (0.25 mM). An attempt to clone the ferripyoverdine receptor gene was made by complementing this growth defect. A number of clones restoring growth of K437 on dipyridyl-containing medium were obtained and several of these restored moderate expression of the 90 kDa receptor. A 5.5 kb Xhol-Hindlll fragment derived from one of these clones was similarly capable of complementing the dipyridyl growth defect although it failed to restore expression of the 90 kDa ferripyoverdine receptor. Nucleotide sequencing of the 5.5kb fragment revealed two large open reading frames (ORFs), designated ORFA and ORFB, which appeared to form an operon and were capable of encoding products of 41 kDa and 112 kDa, respectively. Using a phage T7-based expression system, products of 42 kDa and c. 108 kDa were produced from the cloned DNA, confirming that the ORFs were, indeed, expressed. The cloned ORFAB operon was inducible under conditions of iron limitation in both P. aeruginosa and Escherichia coli. In addition, mutants expressing ORFAB constitutively were constitutive for pyoverdine and ferripyoverdine receptor production suggesting that components of the pyoverdine-mediated iron-transport system are co-regulated with ORFAB. The predicted products of ORFA and ORFB showed significant homology to the Escherichia coli EnvC and EnvD polypeptides which are reportedly involved in septum formation. In addition, the ORFB product showed moderate homology to the CzcA polypeptide identified as a component of a membrane-associated plasmid-encoded cation efflux system in Alcaligenes eutrophus. Using in vitro mutagenesis and gene replacement, ORFA- and ORFB-deficient mutants of K372, the parent... [ABSTRACT FROM AUTHOR]

Expression of the ferric enterobactin receptor in Pseudomonas aeruginosa is inducible by enterobactin and requires sequences upstream of the structural gene (pfeA). Nucleotide sequencing of a 2.5 kilobase pair (kb) region of DNA immediately upstream of pfeA revealed two open reading frames (ORFs), pfeR and pfeS, which appeared to comprise an operon. The predicted products of pfeR and pfeS (molecular weight 26796 and 50597, respectively) exhibited a high degree of homology to response-regulator and sensor components, respectively, of the superfamily of prokaryotic environmentally responsive protein pairs. Consistent with an apparent role in regulating expression of plea in response to enterobactin, introduction of pfeR/pfeS into P. aeruginosa on a high-copy-number vector enhanced enterobactin-dependent expression of pfeA. Furthermore, a pfeR mutant obtained by in vitro mutagenesis and gene replacement failed to express PfeA despite the presence of enterobactin in the culture medium. Analysis of the hydropathy profiles of PfeR and PfeS supported a cytoplasmic location for PfeR and a cytoplasmic membrane location for PfeS. [ABSTRACT FROM AUTHOR]

Recent research by Rabinowitz and Macdonald (1989) claims that voting behavior is better accounted for by a directional model than by a traditional proximity or Euclidean model. This paper compares directional and Euclidean models using congressional roll-call voting data. For these relatively well-informed voters, we can unambiguously reject the directional model in favor of the traditional Euclidean spatial model. We conclude that congressional voting can indeed be very accurately represented by the Euclidean model. [ABSTRACT FROM AUTHOR]

This paper surveys recent developments in analytical models of roll-call voting in the U.S. Congress. Two controversies are analyzed in the paper: the one over the number of evaluative dimensions that underlie congressional voting and the other over the relative importance of the legislator's ideology and the objective economic interests of the constituency. The framework for the analysis is a spatial theory of voting, which embodies Philip Converse's theory of belief systems. [ABSTRACT FROM AUTHOR]

This article proposes stochastic, spatial model of roll-call voting as a benchmark for evaluating more complex models of congressional behavior. On the basis of several evaluative criteria, this model outperforms Weisberg's two-party and three-party models and Hammond and Fraser's random-voting models. Particularly, the spatial model successfully recovers the occurrences of hurrah, party unity, conservative coalition, and Civil War votes as well as the marginal distribution of yea votes. At the same time, the spatial model is parsimonious, requiring that more parameters be estimated than the two-party model does but fewer than the three-party model. [ABSTRACT FROM AUTHOR]