On the Khalfin's improvement of the LOY effective Hamiltonian for neutral meson complex

The general properties of the effective Hamiltonian for neutral meson system improved by L.A. Khalfin in 1980 are studied. It is shown that contrary to the standard result of the Lee--Oehme--Yang (LOY) theory, the diagonal matrix elements of this effective Hamiltonian can not be equal in a CPT invariant system. It is also shown that the scalar product of short, $|K_{S}>$, and long, $|K_{L}>$, living superpositions of neutral kaons can not be real when CPT symmetry is conserved in the system under considerations whereas within the LOY theory such a scalar product is real.Comment: LaTeX2e, 25 pages, new comment and references adde

Unsung heroes: who supports social work students on placement?

Since the introduction of the three year degree programme in 2003, social work education has undergone a number of significant changes. The time students spend on placement has been increased to two hundred days, and the range of placement opportunities and the way in which these placements have been configured has significantly diversified. A consistent feature over the years, however, has been the presence of a Practice Educator (PE) who has guided, assessed and taught the student whilst on placement. Unsurprisingly, the role of the PE and the pivotal relationship they have with the student has been explored in the past and features in social work literature. This paper, however, concentrates on a range of other relationships which are of significance in providing support to students on placement. In particular it draws on research to discuss the role of the university contact tutor, the place of the wider team in which the student is sited, and the support offered by family, friends and others. Placements and the work undertaken by PE’s will continue to be integral to the delivery of social work education. It is, however, essential to recognise and value the often over looked role of others in providing support to students on placement

Vfr Directly Activates exsA Transcription To Regulate Expression of the Pseudomonas aeruginosa Type III Secretion System

ABSTRACT The Pseudomonas aeruginosa cyclic AMP (cAMP)-Vfr system (CVS) is a global regulator of virulence gene expression. Regulatory targets include type IV pili, secreted proteases, and the type III secretion system (T3SS). The mechanism by which CVS regulates T3SS gene expression remains undefined. Single-cell expression studies previously found that only a portion of the cells within a population express the T3SS under inducing conditions, a property known as bistability. We now report that bistability is altered in a vfr mutant, wherein a substantially smaller fraction of the cells express the T3SS relative to the parental strain. Since bistability usually involves positive-feedback loops, we tested the hypothesis that virulence factor regulator (Vfr) regulates the expression of exsA . ExsA is the central regulator of T3SS gene expression and autoregulates its own expression. Although exsA is the last gene of the exsCEBA polycistronic mRNA, we demonstrate that Vfr directly activates exsA transcription from a second promoter (P exsA ) located immediately upstream of exsA . P exsA promoter activity is entirely Vfr dependent. Direct binding of Vfr to a P exsA promoter probe was demonstrated by electrophoretic mobility shift assays, and DNase I footprinting revealed an area of protection that coincides with a putative Vfr consensus-binding site. Mutagenesis of that site disrupted Vfr binding and P exsA promoter activity. We conclude that Vfr contributes to T3SS gene expression through activation of the P exsA promoter, which is internal to the previously characterized exsCEBA operon. IMPORTANCE Vfr is a cAMP-dependent DNA-binding protein that functions as a global regulator of virulence gene expression in Pseudomonas aeruginosa . Regulation by Vfr allows for the coordinate production of related virulence functions, such as type IV pili and type III secretion, required for adherence to and intoxication of host cells, respectively. Although the molecular mechanism of Vfr regulation has been defined for many target genes, a direct link between Vfr and T3SS gene expression had not been established. In the present study, we report that Vfr directly controls exsA transcription, the master regulator of T3SS gene expression, from a newly identified promoter located immediately upstream of exsA

Young Stellar Object Candidates in IC 417

IC 417 is in the Galactic Plane, and likely part of the Aur OB2 association; it is ~2 kpc away. Stock 8 is one of the densest cluster constituents; off of it to the East, there is a 'Nebulous Stream' (NS) that is dramatic in the infrared (IR). We have assembled a list of literature-identified young stellar objects (YSOs), new candidate YSOs from the NS, and new candidate YSOs from IR excesses. We vetted this list via inspection of the images, spectral energy distributions (SEDs), and color-color/color-magnitude diagrams. We placed the 710 surviving YSOs and candidate YSOs in ranked bins, nearly two-thirds of which have more than 20 points defining their SEDs. The lowest-ranked bins include stars that are confused, or likely carbon stars. There are 503 in the higher-ranked bins; half are SED Class III, and $\sim$40\% are SED Class II. Our results agree with the literature in that we find that the NS and Stock 8 are at about the same distance as each other (and as the rest of the YSOs), and that the NS is the youngest region, with Stock 8 a little older. We do not find any evidence for an age spread within the NS, consistent with the idea that the star formation trigger came from the north. We do not find that the other literature-identified clusters here are as young as either the NS or Stock 8; at best they are older than Stock 8, and they may not all be legitimate clusters.Comment: Accepted by AAS Journal

ESCRT ubiquitin-binding domains function cooperatively during MVB cargo sorting

Ubiquitin (Ub) sorting receptors facilitate the targeting of ubiquitinated membrane proteins into multivesicular bodies (MVBs). Ub-binding domains (UBDs) have been described in several endosomal sorting complexes required for transport (ESCRT). Using available structural information, we have investigated the role of the multiple UBDs within ESCRTs during MVB cargo selection. We found a novel UBD within ESCRT-I and show that it contributes to MVB sorting in concert with the known UBDs within the ESCRT complexes. These experiments reveal an unexpected level of coordination among the ESCRT UBDs, suggesting that they collectively recognize a diverse set of cargo rather than act sequentially at discrete steps

The AlgZR Two-Component System Recalibrates the RsmAYZ Posttranscriptional Regulatory System To Inhibit Expression of the Pseudomonas aeruginosa Type III Secretion System

Pseudomonas aeruginosa causes chronic airway infections in cystic fibrosis (CF) patients. A classic feature of CF airway isolates is the mucoid phenotype. Mucoidy arises through mutation of the mucA anti-sigma factor and subsequent activation of the AlgU regulon. Inactivation of mucA also results in reduced expression of the Vfr transcription factor. Vfr regulates several important virulence factors, including a type III secretion system (T3SS). In the present study, we report that ExsA expression, the master regulator of T3SS gene expression, is further reduced in mucA mutants through a Vfr-independent mechanism involving the RsmAYZ regulatory system. RsmA is an RNA binding protein required for T3SS gene expression. Genetic experiments suggest that the AlgZR two-component system, part of the AlgU regulon, inhibits ExsA expression by increasing the expression of RsmY and RsmZ, two small noncoding RNAs that sequester RsmA from target mRNAs. Epistasis analyses revealed that increasing the concentration of free RsmA, through either rsmYZ deletion or increased RsmA expression, partially restored T3SS gene expression in the mucA mutant. Furthermore, increasing RsmA availability in combination with Vfr complementation fully restored T3SS expression. Recalibration of the RsmAYZ system by AlgZR, however, did not alter the expression of other selected RsmA-dependent targets. We account for this observation by showing that ExsA expression is more sensitive to changes in free RsmA than other members of the RsmA regulon. Together, these data indicate that recalibration of the RsmAYZ system partially accounts for reduced T3SS gene expression in mucA mutants

Metabolic Adaptation of Ralstonia solanacearum during Plant Infection: A Methionine Biosynthesis Case Study

MetE and MetH are two distinct enzymes that catalyze a similar biochemical reaction during the last step of methionine biosynthesis, MetH being a cobalamin-dependent enzyme whereas MetE activity is cobalamin-independent. In this work, we show that the last step of methionine synthesis in the plant pathogen Ralstonia solanacearum is under the transcriptional control of the master pathogenicity regulator HrpG. This control is exerted essentially on metE expression through the intermediate regulator MetR. Expression of metE is strongly and specifically induced in the presence of plant cells in a hrpG- and metR-dependent manner. metE and metR mutants are not auxotrophic for methionine and not affected for growth inside the plant but produce significantly reduced disease symptoms on tomato whereas disruption of metH has no impact on pathogenicity. The finding that the pathogen preferentially induces metE expression rather than metH in the presence of plant cells is indicative of a probable metabolic adaptation to physiological host conditions since this induction of metE occurs in an environment in which cobalamin, the required co-factor for MetH, is absent. It also shows that MetE and MetH are not functionally redundant and are deployed during specific stages of the bacteria lifecycle, the expression of metE and metH being controlled by multiple and distinct signals

An unusual CsrA family member operates in series with RsmA to amplify posttranscriptional responses in Pseudomonas aeruginosa

Members of the CsrA family of prokaryotic mRNA-binding proteins alter the translation and/or stability of transcripts needed for numerous global physiological processes. The previously described CsrA family member in Pseudomonas aeruginosa (RsmA) plays a central role in determining infection modality by reciprocally regulating processes associated with acute (type III secretion and motility) and chronic (type VI secretion and biofilm formation) infection. Here we describe a second, structurally distinct RsmA homolog in P. aeruginosa (RsmF) that has an overlapping yet unique regulatory role. RsmF deviates from the canonical 5 β-strand and carboxyl-terminal α-helix topology of all other CsrA proteins by having the α-helix internally positioned. Despite striking changes in topology, RsmF adopts a tertiary structure similar to other CsrA family members and binds a subset of RsmA mRNA targets, suggesting that RsmF activity is mediated through a conserved mechanism of RNA recognition. Whereas deletion of rsmF alone had little effect on RsmA-regulated processes, strains lacking both rsmA and rsmF exhibited enhanced RsmA phenotypes for markers of both type III and type VI secretion systems. In addition, simultaneous deletion of rsmA and rsmF resulted in superior biofilm formation relative to the wild-type or rsmA strains. We show that RsmF translation is derepressed in an rsmA mutant and demonstrate that RsmA specifically binds to rsmF mRNA in vitro, creating a global hierarchical regulatory cascade that operates at the posttranscriptional level