The apical complex of Toxoplasma gondii is widely believed to serve essential functions in both invasion of its host cells (including human cells), and in replication of the parasite. The understanding of apical complex function, the basis for its novel structure, and the mechanism for its motility are greatly impeded by lack of knowledge of its molecular composition. We have partially purified the conoid/apical complex, identified ~200 proteins that represent 70% of its cytoskeletal protein components, characterized seven novel proteins, and determined the sequence of recruitment of five of these proteins into the cytoskeleton during cell division. Our results provide new markers for the different subcompartments within the apical complex, and revealed previously unknown cellular compartments, which facilitate our understanding of how the invasion machinery is built. Surprisingly, the extreme apical and extreme basal structures of this highly polarized cell originate in the same location and at the same time very early during parasite replication.

Cell migration requires the transmission of motion generated in the actin cytoskeleton to the extracellular environment through a complex assembly of proteins in focal adhesions. We developed correlational fluorescent speckle microscopy to measure the coupling of focal-adhesion proteins to actin filaments. Different classes of focal-adhesion structural and regulatory molecules exhibited varying degrees of correlated motions with actin filaments, indicating hierarchical transmission of actin motion through focal adhesions. Interactions between vinculin, talin, and actin filaments appear to constitute a slippage interface between the cytoskeleton and integrins, generating a molecular clutch that is regulated during the morphodynamic transitions of cell migration.

H epatitis C virus (HCV) has emerged as the major etiological agent of liver disease. Approximately 170 million individuals are infected worldwide, and the majority are at risk for developing serious progressive liver disease, with HCV being the leading indication for liver transplantation. The HCV single-stranded RNA genome encodes a single polyprotein, which is cleaved by viral and cellular proteases to produce the structural proteins; core E1 and E2 and nonstructural proteins; p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B. The only approved treatment for HCV infection is interferon-␣ in combination with ribavirin, which is toxic and only effective in 50% of individuals with genotype I infections. Clearly, there is a need for more effective therapies and for the development of prophylactic and/or therapeutic vaccines.Cellular and humoral responses are generated during acute infection, but they are insufficient to achieve viral clearance in the majority of individuals, with approximately 60%-80% of new infections becoming persistent. 1,2 Neutralizing antibody (nAb) responses often provide the first-line adaptive defense against infection by limiting virus spread. However, little is known about the impact of the humoral immune response on HCV pathobiology. Serum antibodies (Abs) from chronically HCVinfected individuals demonstrate broadly reactive neutralizing properties in vitro and yet fail to control viral infection in vivo. [3][4][5] The reasons for their lack of effect are poorly understood. HCV may escape neutralization by

results in partitioning of the apicoplast, nucleus, endoplasmic reticulum, and finally the mitochondrion, which enters the developing daughters rapidly, but only very late during the division cycle. The specialized secretory organelles (micronemes and rhoptries) form de novo. This distinctive pattern of replication -in which organellar segregation spans ~75% of the cell cycle, completely encompassing S phase -suggests an unusual mechanism of cell cycle regulation. Supplementary material available online at

Toxoplasma gondii is an obligatory intracellular parasite, an important human pathogen, and a convenient laboratory model for many other human and veterinary pathogens in the phylum Apicomplexa, such as Plasmodium, Eimeria, and Cryptosporidia. 22 subpellicular microtubules form a scaffold that defines the cell shape of T. gondii. Its cytoskeleton also includes an intricate apical structure consisting of the conoid, two intraconoid microtubules, and two polar rings. The conoid is a 380-nm diameter motile organelle, consisting of fibers wound into a spiral like a compressed spring. FRAP analysis of transgenic T. gondii expressing YFP-α-tubulin reveals that the conoid fibers are assembled by rapid incorporation of tubulin subunits during early, but not late, stages of cell division. Electron microscopic analysis shows that in the mature conoid, tubulin is arranged into a novel polymer form that is quite different from typical microtubules.