The Saccharomyces cerevisiae LEP1/SAC3 gene is associated with leucine transport

Leucine uptake by Saccharomyces cerevisiae is mediated by three transport systems, the general amino acid transport system (GAP), encoded by GAP1, and two group-specific systems (S1 and S2), which also transport isoleucine and valine. A new mutant defective in both group-specific transport activities was isolated by employing a gap1 leu4 strain and selecting for trifluoroleucine-resistant mutants which also showed greatly reduced ability to utilize l-leucine as sole nitrogen source and very low levels of [¹⁴C]l-leucine uptake. A multicopy plasmid containing a DNA fragment which complemented the leucine transport defect was isolated by selecting for transformants that grew normally on minimal medium containing leucine as nitrogen source and subsequently assaying [¹⁴C]l-leucine uptake. Transformation of one such mutant, lep1, restored sensitivity to trifluoroleucine. The complementing gene, designated LEP1, was subcloned and sequenced. The LEP1 ORF encodes a large protein that lacks characteristics of a transporter or permease (i.e., lacks hydrophobic domains necessary for membrane association). Instead, Lep1p is a very basic protein (pI of 9.2) that contains a putative bipartite signal sequence for targeting to the nucleus, suggesting that it might be a DNA-binding protein. A database search revealed that LEP1 encodes a polypeptide that is identical to Sac3p except for an N-terminal truncation. The original identification of SAC3 was based on the isolation of a mutant allele, sac3-1, that suppresses the temperature-sensitive growth defect of an actin mutant containing the allele act1-1. Sac3p has been previously shown to be localized in the nucleus. When a lep1 mutant was crossed with a sac3 deletion mutant, no complementation was observed, indicating that the two mutations are functionally allelic. Received: 6 January 1999 / Accepted: 4 June 1999     

Have wing morphology or flight kinematics evolved for extreme high altitude migration in the bar-headed goose?

Bar-headed geese (Anser indicus) migrate over the Himalayan mountains, at altitudes up to 9000 m above sea level, where air density and oxygen availability are extremely low. This study determined whether alterations in wing morphology or wingbeat frequency during free flight have evolved in this species to facilitate extreme high altitude migration, by comparing it to several closely related goose species. Wingspan and wing loading scaled near isometrically with body mass across all species (with power scaling exponents of 0.22 and 0.47, respectively), and wingbeat frequency scaled negatively to mass (scaling exponent of -0.167). Bar-headed geese had the largest wingspan residual and smallest wing loading residual from these allometric relationships, suggesting that they are at the top end of the wing size distribution. These morphological characters of bar-headed geese were not outside the normal variation exhibited by low altitude species, however, being within the prediction intervals of the regression. This was particularly true after the data were corrected for phylogeny using the independent contrasts method. Wingbeat frequencies of bar-headed geese during steady flight were the same as low altitude geese, both with and without correcting for phylogeny. Without adjusting other kinematic features (e.g., wing motion and generated wake structure) to supplement lift generation in low air densities, the metabolic costs of flight in bar-headed geese at high altitude could exceed the already high costs at sea level. The apparent lack of morphological and kinematic adaptation emphasizes the importance of physiological adaptations for enhancing oxygen transport and utilization in this species.     

Rationale and design of the Edwards SAPIEN-3 periprosthetic leakage evaluation versus Medtronic CoreValve in transfemoral aortic valve implantation (ELECT) trial

Background and objectives

Periprosthetic aortic regurgitation (PPR) after transcatheter aortic valve implantation (TAVI) remains an important issue associated with impaired long-term outcomes. The current randomised study aims to evaluate potential differences between the balloon-expandable Edwards SAPIEN-3 and the self-expanding Medtronic CoreValve system with the main focus on post-TAVI PPR by means of novel imaging endpoints, and an additional focus on other clinical endpoints.

Endpoints

The primary endpoint of this study is quantitative assessment of the severity of post-procedural PPR using cardiac magnetic resonance imaging. Several other novel imaging modalities (X-ray contrast angiography, echocardiography) are used as secondary imaging modalities for the assessment of PPR following TAVI. Secondary objectives of the study include clinical outcomes such as cerebral and kidney injury related to TAVI, and quality of life.

Methods and design

The ELECT study is a single-centre, prospective, two-armed randomised controlled trial. For the purpose of this study, 108 consecutive adult patients suitable for transfemoral TAVI will be randomly allocated to receive the SAPIEN-3 (n = 54) or the CoreValve system (n = 54).

Discussion

The ELECT trial is the first randomised controlled trial to quantitatively compare the extent of post-TAVI PPR between the SAPIEN-3 and CoreValve. Furthermore, it will evaluate potential differences between the two prostheses with regard to mid-term clinical outcome and quality of life.

     

Evolutionary engineering of Corynebacterium glutamicum

A unique feature of biotechnology is that we can harness the power of evolution to improve process performance. Rational engineering of microbial strains has led to the establishment of a variety of successful bioprocesses, but it is hampered by the overwhelming complexity of biological systems. Evolutionary engineering represents a straightforward approach for fitness‐linked phenotypes (e.g., growth or stress tolerance) and is successfully applied to select for strains with improved properties for particular industrial applications. In recent years, synthetic evolution strategies have enabled selection for increased small molecule production by linking metabolic productivity to growth as a selectable trait. This review summarizes the evolutionary engineering strategies performed with the industrial platform organism Corynebacterium glutamicum. An increasing number of recent studies highlight the potential of adaptive laboratory evolution (ALE) to improve growth or stress resistance, implement the utilization of alternative carbon sources, or improve small molecule production. Advances in next‐generation sequencing and automation technologies will foster the application of ALE strategies to streamline microbial strains for bioproduction and enhance our understanding of biological systems.     

The mechanosensitive channel protein MscL is targeted by the SRP to the novel YidC membrane insertion pathway of Escherichia coli

The mechanosensitive channel MscL in the inner membrane of Escherichia coli is a homopentameric complex involved in homeostasis when cells are exposed to hypo-osmotic conditions. The E. coli MscL protein is synthesized as a polypeptide of 136 amino acid residues and uses the bacterial signal recognition particle (SRP) for membrane targeting. The protein is inserted into the membrane independently of the Sec translocon. Mutants affected in the Sec-components are competent for MscL assembly. Translocation of the periplasmic domain was detected using a membrane-impermeant, sulfhydryl-specific gel-shift reagent. The modification of a single cysteine residue at position 68 indicated its translocation across the inner membrane. From these in vivo experiments, it is concluded that the electrical chemical membrane potential is not necessary for membrane insertion of MscL. However, depletion of the membrane insertase YidC inhibits translocation of the protein across the membrane. We show here that YidC is essential for efficient membrane insertion of the MscL protein. YidC is a component of a recently identified membrane insertion pathway that is evolutionarily conserved in bacteria, mitochondria and chloroplasts.     

Adenosine receptor expression in the adult zebrafish retina

Purinergic Signalling - Adenosine is an endogenous nucleoside in the central nervous system that acts on adenosine receptors. These are G protein-coupled receptors that have four known subtypes:...     

Transcatheter aortic valve implantation amid the COVID-19 pandemic: a nationwide analysis of the first COVID-19 wave in the Netherlands

IntroductionThe coronavirus disease 2019 (COVID-19) pandemic has put tremendous pressure on healthcare systems. Most transcatheter aortic valve implantation (TAVI) centres have adopted different triage systems and procedural strategies to serve highest-risk patients first and to minimise the burden on hospital logistics and personnel. We therefore assessed the impact of the COVID-19 pandemic on patient selection, type of anaesthesia and outcomes after TAVI.MethodsWe used data from the Netherlands Heart Registration to examine all patients who underwent TAVI between March 2020 and July 2020 (COVID cohort), and between March 2019 and July 2019 (pre-COVID cohort). We compared patient characteristics, procedural characteristics and clinical outcomes.ResultsWe examined 2131 patients who underwent TAVI (1020 patients in COVID cohort, 1111 patients in pre-COVID cohort). EuroSCORE II was comparable between cohorts (COVID 4.5 ± 4.0 vs pre-COVID 4.6 ± 4.2, p = 0.356). The number of TAVI procedures under general anaesthesia was lower in the COVID cohort (35.2% vs 46.5%, p < 0.001). Incidences of stroke (COVID 2.7% vs pre-COVID 1.7%, p = 0.134), major vascular complications (2.3% vs 3.4%, p = 0.170) and permanent pacemaker implantation (10.0% vs 9.4%, p = 0.634) did not differ between cohorts. Thirty-day and 150-day mortality were comparable (2.8% vs 2.2%, p = 0.359 and 5.2% vs 5.2%, p = 0.993, respectively).ConclusionsDuring the COVID-19 pandemic, patient characteristics and outcomes after TAVI were not different than before the pandemic. This highlights the fact that TAVI procedures can be safely performed during the COVID-19 pandemic, without an increased risk of complications or mortality.Supplementary InformationThe online version of this article (10.1007/s12471-022-01704-9) contains supplementary material, which is available to authorized users.     

Ecotypic variation in plant characteristics for Origanum vulgare subsp. hirtum populations

Origanum vulgare L. subsp. hirtum (Link) Ietsw. is a polymorphic taxon with respect to essential oil production and glandular trichome density. Here it is examined whether the natural populations that are indigenous in continental Greece may be considered as different ecotypes (i.e. populations with different genetic variation) and whether evidence regarding a fitness cost from essential oil production could be obtained. Samples from 30 different natural populations, differing in climatic conditions, were collected across continental Greece in 1998–2000 and were studied for essential oil production and glandular trichome density. Additionally, individual plants, derived from propagated rhizomes, originated from the natural populations, were transplanted in pots in two gardens that varied in terms of mean temperature and aridity. In these experimental populations, the above-ground phytomass and ratio of leaves and inflorescences to above-ground phytomass were additionally measured. The main findings of the study were (a) a strong positive correlation between essential oil concentration and glandular trichome density, (b) a high positive correlation between natural and experimental populations in essential oil concentration (or glandular trichome density), (c) a negative correlation between essential oil concentration and phytomass and (d) a positive relationship between the essential oil concentration and the factors thermal status and summer drought of the location of origin. Results suggest that the examined populations of O. vulgare subsp. hirtum are different ecotypes, the production of essential oils has a cost to plant growth and that the prime target of selection, by producing these oils, is to increase the resistance to drought and heat stresses.