Effectiveness of translation coupling in hybrid operons

The possibility of creating artificial overlappons was studied on the model of two genes, that coding for the N-terminal part of lambda cro protein and the cat of E. coli. To test the dependence of translational coupling efficiency on the intercistronic region a series of recombinant DNA molecules carrying different hybrid operons with partially overlapping genes was constructed. The translational efficiency of the distal to the promoter gene was shown to depend on the intercistronic region structure: overlapping of the AUG codon with the terminating one of the proximal gene in the UGAUG manner is optimal for the translational coupling, and the displacement of AUG at several nucleotides in both directions decreases the translational reinitiation efficiency for the ribosomes, that have synthesised the first gene product.     

Bacterial chemotaxis in a two-dimensional attractant gradient

The motion of a population of chemotactic bacteria in a radial exponential gradient of attractant in a cylindrical container has been calculated using a mathematical model suggested by Keller and Segel. Numerical solutions for the equations of bacterial migration have been found which give for all times the cell density at distances from the center of the cylinder. The ultimate distribution of bacteria is a simple stationary exponential function of the distance. Experiments to verify the theoretical predictions are suggested.     

Regular proteinaceous layers ofThermococcus stetteri cell envelope

Proteinaceous layers of theThermococcus stetteri cell envelope were investigated and found to consist of regularly arrayed subunits 18 nm in diameter. According to the results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two major proteins were present. They were glycosylated and had molecular weights of 80,000 and 210,000. In addition to two external regular proteinaceous layers, cells ofT. stetteri were found to have internal regular layers tightly attached to the cytoplasmic membrane. In the region of flagella attachment to the cell, polar membrane-like structures were found in the cytoplasm.     

A model for traveling bands of chemotactic bacteria.

A theoretical model is used to study band formation by chemotactic populations of Escherichia coli. The model includes the bacterial response to attractant gradients, the chemotactic sensitivity of the bacteria to the concentration of the attractant, and population growth. For certain values of the parameters in the model, traveling bands of bacteria form and propagate with or without growth. Under specific growth conditions the band profile is maintained and the band propagates at constant speed. These predictions are in general agreement with the experiment results of J. Adler and earlier theoretical work by L. Segel and his collaborators. However, our theory differs in several important respects from the latter efforts. Suggestions are made for further experiments to test the proposed model and to clarify the nature of the processes which lead to band formation.     

Construction of the plasmid for expression of ETA-EGFP fusion protein under control of the cytomegalovirus promoter and its effects in HeLa cells

Tumor-targeted vectors encoding toxic protein genes are promising tools for treating malignant tumors. We used the pEGFP-N1 vector to construct a novel plasmid (pCMV-ETA-EGFP) for eukaryotic expression of a truncated Pseudomonas aeruginosa exotoxin A (ETA) that is known to inhibit protein synthesis, and subsequently induce cell death, by inactivation of elongation factor-2. ETA was linked to the enhanced green fluorescent protein (EGFP) gene, and ETA-EGFP gene expression was driven by the cytomegalovirus (CMV) promoter. The time-lapse effects of pCMV-ETA-EGFP expression were examined in transiently transfected HeLa cells. HeLa cells transfected with pCMV-ETA-EGFP or cotransfected with pCMV-ETA-EGFP and рЕGFP-N1 showed lower fluorescence intensity than cells transfected with pEGFP-N1 alone. Analysis of the number of dead cells further confirmed the highly toxic effect of the ETA-EGFP fusion protein on cells transfected with pCMV-ETA-EGFP or cotransfected with pCMV-ETA-EGFP and рЕGFP-N1. ETA-EGFP fusion protein induced apoptotic cell death through the caspase-3 activation. By using the antibody against a marker nucleolar antigen A3 [Grigoryev, A.A., Bulycheva, T.I., Sheval, E.V., Kalinina, I.A., Zatsepina, O.V., 2008. Cytological indicators of the overall suppression of protein synthesis revealed by staining with new monoclonal antibody. Cell Tissue Biol. 2, 191–199], the distribution of which changes when HeLa cells are treated with known translation inhibitors, we obtained evidence to support the idea that protein synthesis is inhibited in transfected cells in situ. ETA-EGFP fusion protein was identified in lysates of transfected cells using anti-GFP-BL antibodies. Collectively, our results indicate that HeLa cells transfected with pCMV-ETA-EGFP synthesize the ETA-EGFP fusion protein that efficiently inhibits protein synthesis, leading to massive cell death by an apoptosis-mediated pathway with a participation of caspase-3. The constructed vector can be used in suicidal gene therapy of cancer and may also be useful for investigating the general effects of translational downregulation in human cancer cells. We also suggest a novel approach for detecting the activity of new vectors in transfected cells, which is based on the redistribution of nucleolar proteins in transfected cells.     

A dual function of the CRISPR-Cas system in bacterial antivirus immunity and DNA repair

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) and the associated proteins (Cas) comprise a system of adaptive immunity against viruses and plasmids in prokaryotes. Cas1 is a CRISPR-associated protein that is common to all CRISPR-containing prokaryotes but its function remains obscure. Here we show that the purified Cas1 protein of Escherichia coli (YgbT) exhibits nuclease activity against single-stranded and branched DNAs including Holliday junctions, replication forks and 5'-flaps. The crystal structure of YgbT and site-directed mutagenesis have revealed the potential active site. Genome-wide screens show that YgbT physically and genetically interacts with key components of DNA repair systems, including recB, recC and ruvB. Consistent with these findings, the ygbT deletion strain showed increased sensitivity to DNA damage and impaired chromosomal segregation. Similar phenotypes were observed in strains with deletion of CRISPR clusters, suggesting that the function of YgbT in repair involves interaction with the CRISPRs. These results show that YgbT belongs to a novel, structurally distinct family of nucleases acting on branched DNAs and suggest that, in addition to antiviral immunity, at least some components of the CRISPR-Cas system have a function in DNA repair.     

A β-Lactam Antibiotic Dampens Excitotoxic Inflammatory CNS Damage in a Mouse Model of Multiple Sclerosis

In multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE), impairment of glial “Excitatory Amino Acid Transporters” (EAATs) together with an excess glutamate-release by invading immune cells causes excitotoxic damage of the central nervous system (CNS). In order to identify pathways to dampen excitotoxic inflammatory CNS damage, we assessed the effects of a β-lactam antibiotic, ceftriaxone, reported to enhance expression of glial EAAT2, in “Myelin Oligodendrocyte Glycoprotein” (MOG)-induced EAE. Ceftriaxone profoundly ameliorated the clinical course of murine MOG-induced EAE both under preventive and therapeutic regimens. However, ceftriaxone had impact neither on EAAT2 protein expression levels in several brain areas, nor on the radioactive glutamate uptake capacity in a mixed primary glial cell-culture and the glutamate-induced uptake currents in a mammalian cell line mediated by EAAT2. Moreover, the clinical effect of ceftriaxone was preserved in the presence of the EAAT2-specific transport inhibitor, dihydrokainate, while dihydrokainate alone caused an aggravated EAE course. This demonstrates the need for sufficient glial glutamate uptake upon an excitotoxic autoimmune inflammatory challenge of the CNS and a molecular target of ceftriaxone other than the glutamate transporter. Ceftriaxone treatment indirectly hampered T cell proliferation and proinflammatory INFγ and IL17 secretion through modulation of myelin-antigen presentation by antigen-presenting cells (APCs) e.g. dendritic cells (DCs) and reduced T cell migration into the CNS in vivo. Taken together, we demonstrate, that a β-lactam antibiotic attenuates disease course and severity in a model of autoimmune CNS inflammation. The mechanisms are reduction of T cell activation by modulation of cellular antigen-presentation and impairment of antigen-specific T cell migration into the CNS rather than or modulation of central glutamate homeostasis.     

Factors Associated with Post-Seasonal Serological Titer and Risk Factors for Infection with the Pandemic A/H1N1 Virus in the French General Population

The CoPanFlu-France cohort of households was set up in 2009 to study the risk factors for infection by the pandemic influenza virus (H1N1pdm) in the French general population. The authors developed an integrative data-driven approach to identify individual, collective and environmental factors associated with the post-seasonal serological H1N1pdm geometric mean titer, and derived a nested case-control analysis to identify risk factors for infection during the first season. This analysis included 1377 subjects (601 households). The GMT for the general population was 47.1 (95% confidence interval (CI): 45.1, 49.2). According to a multivariable analysis, pandemic vaccination, seasonal vaccination in 2009, recent history of influenza-like illness, asthma, chronic obstructive pulmonary disease, social contacts at school and use of public transports by the local population were associated with a higher GMT, whereas history of smoking was associated with a lower GMT. Additionally, young age at inclusion and risk perception of exposure to the virus at work were identified as possible risk factors, whereas presence of an air humidifier in the living room was a possible protective factor. These findings will be interpreted in light of the longitudinal analyses of this ongoing cohort.     

Alteration of Tropomyosin-binding Properties of Tropomodulin-1 Affects Its Capping Ability and Localization in Skeletal Myocytes

Tropomodulin (Tmod) is an actin-capping protein that binds to the two tropomyosins (TM) at the pointed end of the actin filament to prevent further actin polymerization and depolymerization. Therefore, understanding the role of Tmod is very important when studying actin filament dependent processes such as muscle contraction and intracellular transport. The capping ability of Tmod is highly influenced by TM and is 1000-fold greater in the presence of TM. There are four Tmod isoforms (Tmod1–4), three of which, Tmod1, Tmod3, and Tmod4, are expressed in skeletal muscles. The affinity of Tmod1 to skeletal striated TM (stTM) is higher than that of Tmod3 and Tmod4 to stTM. In this study, we tested mutations in the TM-binding sites of Tmod1, using circular dichroism (CD) and prediction analysis (PONDR). The mutations R11K, D12N, and Q144K were chosen because they decreased the affinity of Tmod1 to stTM, making it similar to that of affinity of Tmod3 and Tmod4 to stTM. Significant reduction of inhibition of actin pointed-end polymerization in the presence of stTM was shown for Tmod1 (R11K/D12N/Q144K) as compared with WT Tmod1. When GFP-Tmod1 and mutants were expressed in primary chicken skeletal myocytes, decreased assembly of Tmod1 mutants was revealed. This indicates a direct correlation between TM-binding and the actin-capping abilities of Tmod. Our data confirmed the hypothesis that assembly of Tmod at the pointed-end of the actin filament depends on its TM-binding affinity.