SecA, an essential component of the general protein secretion pathway of bacteria, is present in Escherichia coli as soluble and membrane-integral forms. Here we show by electron microscopy that SecA assumes two characteristic forms in the presence of phospholipid monolayers: dumbbell-shaped elongated structures and ring-like pore structures. The ring-like pore structures with diameters of 8 nm and holes of 2 nm are found only in the presence of anionic phospholipids. These ring-like pore structures with larger 3-to 6-nm holes (without staining) were also observed by atomic force microscopic examination. They do not form in solution or in the presence of uncharged phosphatidylcholine. These ring-like phospholipidinduced pore-structures may form the core of bacterial proteinconducting channels through bacterial membranes. The Escherichia coli SecA, a homodimer of 102-kDa subunits in solution, along with SecYEG and other Sec proteins (1-6) are intrinsic components of the protein secretion machinery. SecA binds precursor proteins, hydrolyzes ATP, and uses the energy of hydrolysis to translocate proteins across the cytoplasmic membrane. SecA lacks hydrophobic stretches sufficiently long to span a membrane (7), but it binds to the membrane and interacts with SecYEG and acidic phospholipids. It may integrate into membrane either by itself or together with other Sec proteins (1,(4)(5)(6)(8)(9)(10)(11)(12)(13)). The prevailing model of protein translocation depicts the SecYEG complex as forming the essential translocation core channel through the membrane, and SecA being a peripheral protein which hydrolyzes ATP to insert and deinsert a 30-kDa domain into the membrane. By cycling on and off the membrane it pushes precursor proteins through the SecYEG channel (4,5, 14). Several findings, however, contest this model (15). Blobel's group showed that reconstituted membranes containing Ͻ1% of the normal level of SecY are active in protein translocation, and suggested that SecY is not the obligatory receptor for SecA and that it may not be essential for protein translocation (16). We confirmed and extended these findings by showing that both SecE-and SecYdeficient membranes are capable of translocating some precursor proteins in vitro, indicating that neither SecE nor SecY is essential for translocating all proteins (17, 18). Moreover, we and others have shown that SecA, which is often referred to as the peripheral subunit of preprotein translocase (4, 5), integrates into membranes (6,8,13,19,20), a fraction of which does not cycle on and off the membrane during translocation (13), and possibly forms an integral part of the protein-conducting channel (6,13,17,20,21).SecA's structure in solution has been studied in some detail (10, 11), and recently the three-dimensional crystals of SecA from Bacillus subtilis were obtained for x-ray structural analysis (22, 23). The structure of SecA within membranes, however, is not well understood. SecA has been shown to assume two membrane-integrated forms, one of which is membrane-specifi...

H9N2 influenza A viruses have become established worldwide in terrestrial poultry and wild birds, and are occasionally transmitted to mammals including humans and pigs. To comprehensively elucidate the genetic and evolutionary characteristics of H9N2 influenza viruses, we performed a large-scale sequence analysis of 571 viral genomes from the NCBI Influenza Virus Resource Database, representing the spectrum of H9N2 influenza viruses isolated from 1966 to 2009. Our study provides a panoramic framework for better understanding the genesis and evolution of H9N2 influenza viruses, and for describing the history of H9N2 viruses circulating in diverse hosts. Panorama phylogenetic analysis of the eight viral gene segments revealed the complexity and diversity of H9N2 influenza viruses. The 571 H9N2 viral genomes were classified into 74 separate lineages, which had marked host and geographical differences in phylogeny. Panorama genotypical analysis also revealed that H9N2 viruses include at least 98 genotypes, which were further divided according to their HA lineages into seven series (A–G). Phylogenetic analysis of the internal genes showed that H9N2 viruses are closely related to H3, H4, H5, H7, H10, and H14 subtype influenza viruses. Our results indicate that H9N2 viruses have undergone extensive reassortments to generate multiple reassortants and genotypes, suggesting that the continued circulation of multiple genotypical H9N2 viruses throughout the world in diverse hosts has the potential to cause future influenza outbreaks in poultry and epidemics in humans. We propose a nomenclature system for identifying and unifying all lineages and genotypes of H9N2 influenza viruses in order to facilitate international communication on the evolution, ecology and epidemiology of H9N2 influenza viruses.

Purpose of this study was to establish a lecithin nanoemulsion (LNE) without any synthetic surfactant as a topical delivery vehicle and to evaluate its topical delivery potential by the following factors: particle size, morphology, viscosity, stability, skin hydration and skin penetration. Experimental results demonstrated that an increasing concentration of soybean lecithin and glycerol resulted in a smaller size LNE droplet and increasing viscosity, respectively. The droplet size of optimized LNE, with the glycerol concentration above 75% (w/w), changed from 92 (F10) to 58 nm (F14). Additionally, LNE, incorporated into o/w cream, improved the skin hydration capacity of the cream significantly with about 2.5-fold increase when the concentration of LNE reached 10%. LNE was also demonstrated to improve the penetrability of Nile red (NR) dye into the dermis layer, when an o/w cream, incorporated with NR-loaded LNE, applied on the abdominal skin of rat in vivo. Specifically, the arbitrary unit (ABU) of fluorescence in the dermis layer that had received the cream with a NR-loaded LNE was about 9.9-fold higher than the cream with a NR-loaded general emulsion (GE). These observations suggest that LNE could be used as a promising topical delivery vehicle for lipophilic compounds.

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