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We demonstrate continuous Sisyphus cooling combined with a continuous loading mechanism used to efficiently slow down and accumulate chromium atoms from a guided beam. While the loading itself is based on a single slowing step, applying a radio frequency field forces the atoms to repeat this step many times resulting in a so-called Sisyphus cooling. This extension allows efficient loading and cooling of atoms from a wide range of initial beam conditions. We study the interplay of the continuous loading and simultaneous Sisyphus cooling in different density regimes. In the case of a low density flux we observe a differential gain in phase-space density of nine orders of magnitude. This makes the presented scheme an ideal tool for reaching collisional densities enabling evaporative cooling—in spite of unfavourable initial conditions.

Let 𝑛 >= 2, 𝑉_𝑟(R^𝑛) be the set of functions with zero integrals over all balls in R^𝑛 of radius 𝑟. Various interpolation problems for the class 𝑉_𝑟(R^𝑛) are studied. In the case when the set of interpolation nodes is finite, we solve the interpolation problem under general conditions. For the problems with infinite set of nodes, some sufficient conditions of solvability are founded. Note that an essential condition is that the definition of the class 𝑉_𝑟(R^𝑛) involves integration over balls. For instance, it can be shown that the analogues of our results in which the class of functions is defined using zero integrals over all shifts of a fixed parallelepiped in R^𝑛 do not hold true.

This paper is devoted to a study of the following version of the mean periodic extension problem: (i) Suppose that 𝑇 ∈ ℰ′ (R^𝑛), 𝑛 ≥ 2, and 𝐸 is a non-empty subset of R^𝑛. Let 𝑓 ∈ 𝐶(𝐸). What conditions guarantee that there is an 𝐹 ∈ 𝐶(R^𝑛) coinciding with 𝑓 on 𝐸, such that 𝐹 *𝑇 = 0 in R^𝑛 ? (ii) If such an extension 𝐹 exists, then estimate the growth of 𝐹 at infinity. In this paper, we present a solution of this problem for a broad class of distributions 𝑇 in the case when 𝐸 is a segment in R^n.

The article for the first time studies the approximation of a function together with its derivatives on the real line by solutions of a multidimensional convolution equation of the form 𝑔 * 𝑇 = 0, where 𝑇 is a given compactly supported radial distribution other than a constant multiplied by the Dirac delta function at zero. The following analogue of the well-known Carleman’s theorem on tangent approximation by entire functions is obtained: if 𝑓 ∈ 𝐶^𝑘(ℝ) for some 𝑘 ∈ ℤ_+ and for any 𝜈 ∈ {0, . . . , 𝑘} there is a finite limit lim 𝑡→+0 (︂𝑑/𝑑𝑡)︂^𝜈 𝑓(ln𝑡), then for an arbitrary positive continuous function 𝜀(𝑡) on ℝ there exists an entire function Φ: ℂ^𝑛 → ℂ, such that Φ|_(ℝ^n) * 𝑇 = 0 and ⃒𝑓^(𝜈)(𝑡) −(︂∂/∂𝑥1)︂^𝜈 Φ(𝑡, 0, . . . , 0)|< 𝜀(𝑒^𝑡) for all 𝑡 ∈ ℝ, 𝜈 ∈ {0, . . . , 𝑘} (Theorem 1). It is shown that when approximating a function on subsets of the real line that do not contain a neighborhood of the point −∞, the condition for the existence of a limit in Theorem 1 can be omitted. In addition, the method of proving Theorem 1 allows one to obtain new results that are of interest for the theory of convolution equations of the indicated type. These are results about the growth of solutions (Corollary 3), on the distribution of values (Theorem 2), and also on the solvability of the interpolation problem for solutions of the convolution equation (Corollary 4).

An assay has been developed that allows the identification of molecules that function as type I IFN antagonists. Using this assay, we have identified an Ebola virus-encoded inhibitor of the type I IFN response, the Ebola virus VP35 protein. The assay relies on the properties of an influenza virus mutant, influenza delNS1 virus, which lacks the NS1 ORF and, therefore, does not produce the NS1 protein. When cells are infected with influenza delNS1 virus, large amounts of type I IFN are produced. As a consequence, influenza delNS1 virus replicates poorly. However, high-efficiency transient transfection of a plasmid encoding a protein that interferes with type I IFN-induced antiviral functions, such as the influenza A virus NS1 protein or the herpes simplex virus protein ICP34.5, rescues growth of influenza delNS1 virus. When plasmids expressing individual Ebola virus proteins were transfected into Madin Darby canine kidney cells, the Ebola virus VP35 protein enhanced influenza delNS1 virus growth more than 100-fold. VP35 subsequently was shown to block double-stranded RNA- and virus-mediated induction of an IFN-stimulated response element reporter gene and to block double-stranded RNA- and virus-mediated induction of the IFN-beta promoter. The Ebola virus VP35 therefore is likely to inhibit induction of type I IFN in Ebola virus-infected cells and may be an important determinant of Ebola virus virulence in vivo.

Ebola virus maturation occurs at the plasma membrane of infected cells and involves the clustering of the viral matrix protein VP40 at the assembly site as well as its interaction with the lipid bilayer. Here we report the X-ray crystal structure of VP40 from Ebola virus at 2.0 A resolution. The crystal structure reveals that Ebola virus VP40 is topologically distinct from all other known viral matrix proteins, consisting of two domains with unique folds, connected by a flexible linker. The C-terminal domain, which is absolutely required for membrane binding, contains large hydrophobic patches that may be involved in the interaction with lipid bilayers. Likewise, a highly basic region is shared between the two domains. The crystal structure reveals how the molecule may be able to switch from a monomeric conformation to a hexameric form, as observed in vitro. Its implications for the assembly process are discussed.

The matrix protein VP40 of Ebola virus is believed to play a central role in viral assembly as it targets the plasma membrane of infected cells and subsequently forms a tightly packed layer on the inner side of the viral envelope. Expression of VP40 in Escherichia coli and subsequent proteolysis yielded two structural variants differing by a C-terminal truncation 114 amino acid residues long. As indicated by chemical cross-linking studies and electron microscopy, the larger polypeptide was present in a monomeric form, whereas the truncated one formed hexamers. When analyzed for their in vitro binding properties, both constructs showed that only monomeric VP40 efficiently associated with membranes containing negatively charged lipids. Membrane association of truncated, hexameric VP40 was inefficient, indicating a membrane-recognition role for the C-terminal part. Based on these observations we propose that assembly of Ebola virus involves the formation of VP40 hexamers that is mediated by the N-terminal part of the polypeptide., (Copyright 2000 Academic Press.)

The matrix protein from Ebola virus is a membrane-associated molecule that plays a role in viral budding. Despite its functional similarity to other viral matrix proteins, it displays no sequence similarity and hence may have a distinct fold. X-ray diffraction quality crystals of the Ebola VP40 matrix protein were grown by the hanging-drop vapour-diffusion method. The crystals belong to the monoclinic space group C2, with unit-cell parameters a = 64.4, b = 91.1, c = 47.9 A, beta = 96.3 degrees. A data set to 1.9 A resolution has been collected using synchrotron radiation. The unit cell contains one molecule of molecular weight 35 kDa per asymmetric unit, with a corresponding volume solvent content of 35%.

Gabon has recently been struck three times by Ebola hemorrhagic fever. The first isolate originating from the 1994 outbreak has been subjected to molecular characterization of its GP and VP24 genes. Sequence analysis demonstrates that the agent, Gabon-94 virus, belongs to subtype Zaire of Ebola virus. The isolate is closely related to the Kikwit-95 isolate, and both viruses seem to have evolved from a progenitor virus different from that of the Zaire-76 isolates. The relatively close relationship of all subtype Zaire viruses isolated at different geographical locations and up to 20 years apart suggests an extreme conservation in the yet unknown natural reservoir of Ebola viruses. The level of genetic variability in the human host might be different as indicated by the comparison of isolates from a single outbreak (Mayinga-76 and Eckron-76), but needs further investigation on clinical material of patients by PCR since both isolates have different levels of passages in tissue culture.

The 3' and 5' ends of Marburg virus (MBG)-specific mRNA species have been determined using reverse transcription-PCR, rapid amplification of cDNA ends, or the reverse ligation-mediated PCR procedure after removal of cap structures with tobacco acid pyrophosphatase. The polyadenylation sites of all MBG-specific mRNAs were strictly conserved and corresponded to the predicted transcriptional stop signals of genomic RNA. Determination of the 5' ends of the mRNA species showed that mRNA synthesis started precisely at the first nucleotide of a highly conserved transcriptional start site. The 5' ends of the mRNA species can build a stable secondary structure with the conserved nucleotides always located in the stem region of a hairpin. Nucleotide substitutions in the conserved 5' regions are accompanied by compensatory mutations of the complementary nucleotide thus leading to a conservation of the secondary structures. Compensatory mutations were also found when 5' ends of mRNA of MBG strain Musoke were compared with MBG strain Popp or the closely related Ebola virus, indicating that the secondary structures will be conserved even if the sequence is altered.