Host outer membrane

Abstract: Studies on the virus-cell interactions have proven valuable in elucidating vital cellular processes. Interestingly, certain virus-host membrane interac- tions found in eukaryotic systems seem also to operate in prokaryotes (Bamford, D.H., M. Romantschuk, and P.J. Somerharju, 1987. EMBO (Eur. Mol. Biol. Organ.) J. 6:1467-1473; Romantschuk, M., V.M. Olkkonen, and D.H. Bamford. 1988. EMBO (Eur. Mol. Biol. Organ.) J. 7:1821-1829). f 6 is an enveloped double-stranded RNA virus infecting a gram-negative bacterium. The vi- ral entry is initiated by fusion between the virus mem- brane and host outer membrane, followed by delivery of the viral nucleocapsid (RNA polymerase complex covered with a protein shell) into the host cytosol via an endocytic-like route. In this study, we analyze the inter- action of the nucleocapsid with the host plasma mem- brane and demonstrate a novel approach for dissecting the early events of the nucleocapsid entry process. The initial binding of the nucleocapsid to the plasma mem- brane is independent of membrane voltage ( DC ) and the K 1 and H 1 gradients. However, the following inter- nalization is dependent on plasma membrane voltage ( DC ), but does not require a high ATP level or K 1 and H 1 gradients. Moreover, the nucleocapsid shell protein, P8, is the viral component mediating the membrane- nucleocapsid interaction.

Abstract: The genetic manipulation of marine double-stranded DNA (dsDNA) bacteriophage PM2 (Corticoviridae) has been limited so far. The isolation of an autonomously replicating DNA element of Pseudoalteromonas haloplanktis TAC125 and construction of a shuttle vector replicating in both Escherichia coli and Pseudoalteromonas enabled us to design a set of conjugative shuttle plasmids encoding tRNA suppressors for amber mutations. Using a host strain carrying a suppressor plasmid allows the introduction and analysis of nonsense mutations in PM2. Here, we describe the isolation and characterization of a suppressor-sensitive PM2 sus2 mutant deficient in the structural protein P10. To infect and replicate, PM2 delivers its 10-kbp genome across the cell envelopes of two gram-negative Pseudoalteromonas species. The events leading to the internalization of the circular supercoiled dsDNA are puzzling. In a poorly understood process that follows receptor recognition, the virion capsid disassembles and the internal membrane fuses with the host outer membrane. While beginning to unravel the mechanism of this process, we found that protein P10 plays an essential role in the host cell penetration.

Abstract: Phage AR1, previously known to infectEscherichia coli O157:H7 with high specificity, was further characterized for its genetic properties. The phage DNA sequences including capsid genes and a putative α-glucosyltransferase gene(α-gt) have been deduced. These sequences are conservative but not identical to those of T4 phage. However, a nonessential gene,SegD, organized within the capsid gene cluster of T4 is missing in the corresponding region of AR1 genome, and this characteristic has not been observed among T-even related phages. The difference between AR1 and T4 was further exemplified by their distinct host ranges. Strains ofE. coli O157:H7 collected from different sources were permissive to AR1 but resistant to T4 that normally infects K-12 strains ofE. coli through contact with the outer membrane protein OmpC. Thus, the O157:H7 strains must have a varied OmpC. Indeed, the OmpC sequence of O157:H7 strains was proved to differ from that of K-12 strains by a total of 15 amino acid substitutions and two gaps (a five-residue deletion and a four-residue insertion). The OmpC molecules are relatively conserved across the gram-negative bacteria, and this is the first time OmpC divergence has been found within the sameE. coli species. Since OmpC is located in the outer membrane and its expression is regulated by environmental conditions, alteration of the structure in pathogenic O157:H7 strains may have biological significance.