IMV Executive Assistant
tel. (612) 624-1926
fax. (612) 625-1108
18-242 Moos Tower
515 Delaware St. SE
Minneapolis, MN 55455
Phone: (612) 624-0667
B.A., St. Olaf College
Ph.D., University of Minnesota
Postdoctoral Research: Cytogam Inc., Phoenix, AZ
My research interest is in viral assembly, using the Bacillus subtilis bacteriophage ø29 as a model system. ø29 is a member of the tailed double-stranded DNA (dsDNA) bacteriophages that includes lambda, SPP1 and T4. Bacteriophages are excellent model systems for discerning the mechanisms of assembly and serve as model systems for similar processes in the medically relevant dsDNA animal viruses, such as herpesvirus and adenovirus. ø29 morphogenesis includes assembly of a precursor capsid (prohead), packaging of the viral genomic DNA into the head, followed by the sequential addition of tail proteins to yield the mature infectious virion. The cascade of conformational changes that drive assembly uncover basic principles of protein-protein, protein-DNA, protein-RNA interactions, and DNA transport. ø29 is a premier model system for mechanistic studies of assembly due to the highly efficient in vitro assembly assays and its relative compositional simplicity.
Recent emphasis has been on determining the molecular mechanism of DNA packaging. During this process, the viral genome is packaged into a prohead, thereby compacting the DNA to near-crystalline density. This remarkable process is driven by a transiently assembled molecular motor that converts energy from ATP hydrolysis into the translocation of DNA. Since they must work against the large entropic and electrostatic forces that resist DNA compaction, these packaging motors are among the most powerful biological motors known. The motor is assembled at a unique vertex of the head and, in ø29, is comprised of the dodecameric head-tail connector, a pentameric ring of viral-encoded prohead RNA (pRNA), and a pentameric ring of the viral packaging ATPase. We employ a highly integrated, multi-disciplinary approach to dissect the mechanism of packaging: in my lab, genetic and biochemical studies of motor components provides functional analysis and are combined with collaborations in structural biology (X-ray crystallography, cryo-EM, and NMR) to provide atomic pictures of the motor and the motor-in-action, and single-molecule laser tweezers analysis to dissect motor dynamics. Recent high-resolution tweezers studies have revealed that the ø29 DNA packaging motor operates via a complex, highly coordinated two-phase mechanism. During the “dwell” phase, DNA is stationary; the five ATPase subunits release ADP from the previous cycle, and bind ATP to re-load the motor. During the “burst” phase, ATP hydrolysis and subsequent Pi release are coupled to a rapid translocation of 10bp of DNA into the viral head. This 10bp “burst” is comprised of four 2.5bp sub-steps, with the “fifth” subunit playing a regulatory role to align the motor each cycle. The strict, sequential order of operation demands significant communication in the motor to achieve this level of coordination.
A particular interest of mine is the role of the novel pentameric pRNA ring in the packaging motor. While the head-tail connector and ATPase protein motor components are common to the dsDNA phages, ø29 and its relatives are distinct in that RNA is an essential part of the DNA packaging motor. Given that the phage motors are carrying out the same essential task, it is likely that the functions provided by pRNA are encoded in sub-domains of the larger motor proteins in the other phages. pRNA is a viral-encoded 174-base transcript that forms a pentameric ring through intermolecular base-pairing between complementary loops of adjacent pRNAs in the ring. Visualization of pRNA in the motor by cryo-EM 3-D reconstruction reveals a ring form with five protruding spokes; it is to these “spokes” that the ATPase assembles into its functional ring form. Recent progress has included the first atomic structures of functional sub-domains of pRNA and assignment of function to the essential loops and bulges of pRNA. Of note was the visualization of RNA superhelices in the crystal structure of a pRNA ring that show this suprastructure is formed by alignment of helical elements from adjacent pRNAs via the intermolecular base-pairing. Functionally, these supehelices would serve to connect all the protein components of the motor (capsid, connector and ATPase), suggesting a potential role in motor communication/coordination. The ultimate goal of this research is to determine the atomic structures and dissect the roles of the individual motor components in the packaging process and understand how they work together and communicate and coordinate with each other to create this elegant motor.
'Wisc-e-sota', a Joint UMN-UW Virology Training Grant Symposium was first held on Friday, Sepbember 20th, 2013 at the Uniiversity of Wisconsin-La Crosse, Cartwright Center. This was the inaugural collaborative symposium of the NIH T32-supported virology training programs at the University of Wisconsin-Madison and the University of Minnesota-Twin Cities. Talks and poster sessions were presented by students, postdocs and faculty. The second UMN-UW Virology Training Grant Symposium will be held in the Fall 2014. Details to follow.
The 2014 IMV Symposium will be held on May 12, 2014 and Mark Denison (Vanderbilt) and Bert Semler (UC-Irvine) will be the Keynote Speakers. Click on the link below to register and submit abstracts.
Read about bacteriophage phi 29 and why it matters.
Explore nearly a century's worth of discovery in the field of virology at the University of Minnesota.
"This Week in Virology" from professor Vincent Racaniello.