The N-terminus promotes oligomerization of the Escherichia coli initiator protein DnaA

Initiation of chromosome replication in Escherichia coli is governed by the interaction of the initiator protein DnaA with the replication origin oriC. Here we present evidence that homo-oligomerization of DnaA via its N-terminus (amino acid residues 1-86) is also essential for initiation. Results from solid-phase protein-binding assays indicate that residues 1-86 (or 1-77) of DnaA are necessary and sufficient for self interaction. Using a 'one-hybrid-system' we found that the DnaA N-terminus can functionally replace the dimerization domain of coliphage lambda cl repressor: a lambdacl-DnaA chimeric protein inhibits lambda plasmid replication as efficiently as lambdacI repressor. DnaA derivatives with deletions in the N-terminus are incapable of supporting chromosome replication from oriC, and, conversely, overexpression of the DnaA N-terminus inhibits initiation in vivo. Together, these results indicate that (i) oligomerization of DnaA N-termini is essential for protein function during initiation, and (ii) oligomerization does not require intramolecular cross-talk with the nucleotide-binding domain III or the DNA-binding domain IV. We propose that E. coli DnaA is composed of largely independent domains - or modules - each contributing a partial, though essential, function to the proper functioning of the 'holoprotein'.     

Effect of cadmium, chromium and copper on symbiotic and free-living Rhizobium leguminosarum biovar trifolii

Abstract Plasmid-minus derivatives of Rhizobium leguminosarum biovar trifolii have been isolated. Cured strains lacked symbiotic properties, however they showed increased heavy metal resistance. In the presence of 70 ppm chromium the parent strain, unlike cured derivatives, is unable to grow explanta but can nevertheless nodulate clover.
We propose that rhizobia can circumvent exposure to the heavy metal by entering the plant roots.
Acetylene reduction tests showed that nodulated plants, grown in the presence of 10 ppm of chromium, had an increased nitrogenase activity compared to the control plants.     

Screening of some Romanian plants for their activity against medically important insects

The effects of the action of extracts from 82 plant species included in 39 families of indigenous flora against the larvae and adults of house fly (Musca domestica), the mosquitoes (Aedes aegypti and Anopheles atroparvus) and the German cockroach (Blattella germanica) are presented. Some of the extracts were prepared from air-dried and ground plant material which was exhaustively extracted with successive solvents of different polarity: ethyl ether, ethyl alcohol and water. Other extracts were prepared either by distillation of the whole water extracts of 24 hours macerated plants or by water extraction from residues of plants remained after distillation. These plant extracts act as toxicants, growth and development and reproduction inhibitors and repellents. The differential responses induced by these plant extracts on assessed insects were influenced by several factors such as the plant species, the solvents used for extractions, the species and the stages of insect life and also the methods employed for evaluation. Some of the tested plants appear to have a great potential for providing safer insect control agents.     

Pathogen-driven selection and worldwide HLA class I diversity

The human leukocyte antigen (HLA; known as MHC in other vertebrates) plays a central role in the recognition and presentation of antigens to the immune system and represents the most polymorphic gene cluster in the human genome [1]. Pathogen-driven balancing selection (PDBS) has been previously hypothesized to explain the remarkable polymorphism in the HLA complex, but there is, as yet, no direct support for this hypothesis [2 and 3]. A straightforward prediction coming out of the PDBS hypothesis is that populations from areas with high pathogen diversity should have increased HLA diversity in relation to their average genomic diversity. We tested this prediction by using HLA class I genetic diversity from 61 human populations. Our results show that human colonization history explains a substantial proportion of HLA genetic diversity worldwide. However, between-population variation at the HLA class I genes is also positively correlated with local pathogen richness (notably for the HLA B gene), thus providing support for the PDBS hypothesis. The proportion of variations explained by pathogen richness is higher for the HLA B gene than for the HLA A and HLA C genes. This is in good agreement with both previous immunological and genetic data suggesting that HLA B could be under a higher selective pressure from pathogens.     

Efficacy of two artemisinin combination therapies for uncomplicated falciparum malaria in children under 5 years, Malakal, Upper Nile, Sudan

Background

The treatment for Plasmodium falciparum malaria in Sudan has been in process of change since 2003. Preceding the change, this study aimed to determine which artemisinin-based combination therapies is more effective to treat uncomplicated malaria in Malakal, Upper Nile, Sudan.

Methods

Clinical trial to assess the efficacy of 2 antimalarial therapies to treat P. falciparum infections in children aged 6–59 months, in a period of 42 days after treatment.

Results

A total of 269 children were followed up to 42 days. Artesunate plus Sulfadoxine/Pyrimethamine (AS+SP) and Artesunate plus Amodiaquine (AS+AQ) were both found to be efficacious in curing malaria infections by rapid elimination of parasites and clearance of fever, in preventing recrudescence and suppressing gametocytaemia. The combination of AS+SP appeared slightly more efficacious than AS+AQ, with 4.4% (4/116) versus 15% (17/113) of patients returning with malaria during the 6-week period after treatment (RR = 0.9, 95% CI 0.81–0.96). PCR analysis identified only one recrudescence which, together with one other early treatment failure, gave efficacy rates of 99.0% for AS+AQ (96/97) and 99.1% for AS+SP (112/113). However, PCR results were incomplete and assuming part of the indeterminate samples were recrudescent infections leads to an estimated efficacy ranging 97–98% for AS+SP and 88–95% for AS+AQ.

Conclusion

These results lead to the recommendation of ACT, and specifically AS+SP, for the treatment of uncomplicated falciparum malaria in this area of Sudan. When implemented, ACT efficacy should be monitored in sentinel sites representing different areas of the country.     

Regional TMPRSS2 V197M Allele Frequencies Are Correlated with COVID-19 Case Fatality Rates

Coronavirus disease, COVID-19 (coronavirus disease 2019), caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), has a higher case fatality rate in European countries than in others, especially East Asian ones. One potential explanation for this regional difference is the diversity of the viral infection efficiency. Here, we analyzed the allele frequencies of a nonsynonymous variant rs12329760 (V197M) in the TMPRSS2 gene, a key enzyme essential for viral infection and found a significant association between the COVID-19 case fatality rate and the V197M allele frequencies, using over 200,000 present-day and ancient genomic samples. East Asian countries have higher V197M allele frequencies than other regions, including European countries which correlates to their lower case fatality rates. Structural and energy calculation analysis of the V197M amino acid change showed that it destabilizes the TMPRSS2 protein, possibly negatively affecting its ACE2 and viral spike protein processing.     

Hydrogen peroxide as a mediator of programmed cell death in the blastocyst

Previous work identified in blastocele fluid a soluble activity which killed embryonal carcinoma cells with trophectodermal potential but not those with embryonic potential [35]. From use of a malignant caricature of the late blastocyst, this toxic activity was postulated to be H2O2 [8]. The purpose of this paper was to determine if blastocele fluid also contained amounts of H2O2 capable of mediating the preferential killing of malignant pretrophectodermal cells (ECa 247). We not only observed that blastocele fluid is not toxic for these cells in the presence of catalase, but that malignant cells with embryonic potential (P19) that normally survive exposure to blastocele fluid become sensitive to it if their intracellular glutathione levels are lowered. Thus, it is concluded that the blastocyst contains amounts of H2O2 toxic to malignant pretrophectodermal cells and that glutathione-dependent mechanisms protect malignant inner cell mass cells with embryonic potential. Apparently, H2O2 production and glutathione-dependent protection mechanisms are developmentally regulated in the inner cell mass. These results are discussed with regards to apoptosis and the regulation of tissue mass.     

Fibronectin Affects Transient MMP2 Gene Expression through DNA Demethylation Changes in Non-Invasive Breast Cancer Cell Lines

Metastasis accounts for more than 90% of cancer deaths. Cells from primary solid tumors may invade adjacent tissues and migrate to distant sites where they establish new colonies. The tumor microenvironment is now recognized as an important participant in the signaling that induces cancer cell migration. An essential process for metastasis is extracellular matrix (ECM) degradation by metalloproteases (MMPs), which allows tumor cells to invade local tissues and to reach blood vessels. The members of this protein family include gelatinase A, or MMP-2, which is responsible for the degradation of type IV collagen, the most abundant component of the basal membrane, that separates epithelial cells in the stroma. It is known that fibronectin is capable of promoting the expression of MMP-2 in MCF7 breast cancer cells in culture. In addition, it was already shown that the MMP2 gene expression is regulated by epigenetic mechanisms. In this work, we showed that fibronectin was able to induce MMP2 expression by 30% decrease in its promoter methylation. In addition, a histone marker for an open chromatin conformation was significantly increased. These results indicate a new role for fibronectin in the communication between cancer cells and the ECM, promoting epigenetic modifications.     

In Silico Designing a Candidate Vaccine Against Breast Cancer

International Journal of Peptide Research and Therapeutics - Breast cancer (BC) is the most common type of women’s cancer with a prevalence of about 25%, although it is rare in men...