Postdoctoral training in molecular virology with Dr. Robert A. Lamb, Northwestern University , Evanston , IL

Ph.D. in Biological Chemistry with Dr. Kevin McEntee, UCLA School of Medicine

B.S. in Honors Biology, University of Illinois , Urbana

Assembly and Budding of Paramyxovirus Particles

Virus particles are vehicles designed to transport genetic information from cell to cell and from host to host. For the enveloped viruses, particles are formed by budding. Buds emerge from discrete sites on cellular membranes, then pinch off to release particles as a result of membrane fission. Prior to budding, different viral components assemble together in a coordinated way and concentrate at cellular membranes. This assembly process allows for the release of particles that are likely to be infectious, as they are densely packed with viral proteins and contain viral genomes. My research group studies assembly and budding of the paramyxoviruses, which comprise a large and diverse group of enveloped RNA viruses that includes a number of important human and animal pathogens.

One strategy that we frequently use in our studies on paramyxovirus assembly and budding involves the generation of recombinant viruses from cloned DNA. By manipulating an infectious DNA clone used to generate virus, we are able to make targeted changes to the viral RNA genome and test what effects these changes have on virus replication. Using this approach, we defined an important role for the cytoplasmic tails of the viral glycoproteins in organizing assembly, as evidenced by recombinant simian virus 5 (SV5) that lacks these cytoplasmic tail sequences and exhibits assembly defects. Our findings support the notion that the viral membrane glycoproteins and the internal viral proteins must interact with each other to coordinate virus assembly.

Another approach used in our laboratory involves the generation of virus-like particles (VLPs) from transfected cells. Efficient production and release of virus particles does not appear to require the full set of viral proteins, as expression of just three of the eight SV5 proteins in cells gives rise to the efficient release of noninfectious VLPs that resemble SV5 virions when viewed by electron microscopy. Similar VLP production schemes should prove especially useful when applied towards the study of highly pathogenic paramyxoviruses, as this will allow the assembly and budding steps of these viruses to be investigated while avoiding the need for rigorous containment systems that must be used when studying the corresponding infectious viruses.

Among the least understood aspects of paramyxovirus replication are the late events of virus budding that allow for the pinching off and release of virus particles by membrane fission. For many retroviruses such as HIV-1, these late steps of budding are accomplished at least in part through manipulation of the host's own budding machinery. When this machinery is re-routed to virus assembly sites via protein-protein interaction domains within viral proteins called late domains, virus budding is facilitated. We recently identified the short peptide sequence FPIV within the matrix protein of SV5 that appears to function as a paramyxovirus late domain. Experiments that aim to identify host protein(s) that bind to SV5 M protein via FPIV are now underway. Once FPIV-binding proteins have been identified, their importance to SV5 budding will be assessed, and their normal functions in uninfected cells will be investigated. Additionally, we are interested in determining the extent to which other paramyxoviruses use FPIV-like sequences as late domains.

Schmitt, A. P., He, B. & Lamb, R. A. (1999). Involvement of the cytoplasmic domain of the hemagglutinin-neuraminidase protein in assembly of the paramyxovirus simian virus 5. J. Virol. 73, 8703-8712.

Schmitt, A. P., Leser, G. P., Waning, D. L. & Lamb, R. A. (2002). Requirements for budding of paramyxovirus simian virus 5 virus-like particles. J. Virol. 76, 3952-3964.

Waning, D.L., Schmitt, A.P., Leser, G.P., and Lamb, R.A. (2002). Roles for the cytoplasmic tails of the fusion and hemagglutinin-neuraminidase proteins in budding of the paramyxovirus simian virus 5. J. Virol. 76, 9284-9297.

Schmitt, A. P. & Lamb, R. A. (2004). Escaping from the Cell: Assembly and Budding of Negative-Strand RNA Viruses. Curr. Top. Microbiol. Immunol. 283, 145-196.

Schmitt, A. P., Leser, G. P., Morita, E., Sundquist, W. I. & Lamb, R. A. (2005). Evidence for a new viral late domain core sequence, FPIV, necessary for budding of a paramyxovirus. J. Virol. 79, 2988-2997.

Schmitt, A.P. & Lamb, R.A. (2005). Influenza virus assembly and budding at the viral budozone. Adv. Virus Res. 64, 383-416.