Phylogenomics of the Reproductive Parasite Wolbachia pipientis wMel: A Streamlined Genome Overrun by Mobile Genetic Elements

The complete sequence of the 1,267,782 bp genome of Wolbachia pipientis wMel, an obligate intracellular bacteria of Drosophila melanogaster, has been determined. Wolbachia, which are found in a variety of invertebrate species, are of great interest due to their diverse interactions with different hosts, which range from many forms of reproductive parasitism to mutualistic symbioses. Analysis of the wMel genome, in particular phylogenomic comparisons with other intracellular bacteria, has revealed many insights into the biology and evolution of wMel and Wolbachia in general. For example, the wMel genome is unique among sequenced obligate intracellular species in both being highly streamlined and containing very high levels of repetitive DNA and mobile DNA elements. This observation, coupled with multiple evolutionary reconstructions, suggests that natural selection is somewhat inefficient in wMel, most likely owing to the occurrence of repeated population bottlenecks. Genome analysis predicts many metabolic differences with the closely related Rickettsia species, including the presence of intact glycolysis and purine synthesis, which may compensate for an inability to obtain ATP directly from its host, as Rickettsia can. Other discoveries include the apparent inability of wMel to synthesize lipopolysaccharide and the presence of the most genes encoding proteins with ankyrin repeat domains of any prokaryotic genome yet sequenced. Despite the ability of wMel to infect the germline of its host, we find no evidence for either recent lateral gene transfer between wMel and D. melanogaster or older transfers between Wolbachia and any host. Evolutionary analysis further supports the hypothesis that mitochondria share a common ancestor with the α-Proteobacteria, but shows little support for the grouping of mitochondria with species in the order Rickettsiales. With the availability of the complete genomes of both species and excellent genetic tools for the host, the wMel–D. melanogaster symbiosis is now an ideal system for studying the biology and evolution of Wolbachia infections

The Transmembrane Domain of the Respiratory Syncytial Virus F Protein Is an Orientation-Independent Apical Plasma Membrane Sorting Sequence

The processes that facilitate transport of integral membrane proteins though the secretory pathway and subsequently target them to particular cellular membranes are relevant to almost every field of biology. These transport processes involve integration of proteins into the membrane of the endoplasmic reticulum (ER), passage from the ER to the Golgi, and post-Golgi trafficking. The respiratory syncytial virus (RSV) fusion (F) protein is a type I integral membrane protein that is uniformly distributed on the surface of infected nonpolarized cells and localizes to the apical plasma membrane of polarized epithelial cells. We expressed wild-type or altered RSV F proteins to gain a better understanding of secretory transport and plasma membrane targeting of type I membrane proteins in polarized and nonpolarized epithelial cells. Our findings reveal a novel, orientation-independent apical plasma membrane targeting function for the transmembrane domain of the RSV F protein in polarized epithelial cells. This work provides a basis for a more complete understanding of the role of the transmembrane domain and cytoplasmic tail of viral type I integral membrane proteins in secretory transport and plasma membrane targeting in polarized and nonpolarized cells