Calander Home 2001-2002 2002-2003 Paul Jardine Looking Under the Hood of a Powerful Molecular Motor Date: September 30 Time: Noon to 1 Place: BSBE 4-101 Bacteriophages have long served as model systems for the study of viral assembly and biological events at the molecular level. The Bacillus subtilis phage phi29 was isolated from the soils of Minnesota forty years ago, and has been developed into the premier model system for the study of virus capsid assembly and DNA packaging. Recent achievements in understanding phi29 assembly result from combining the approaches of biochemistry and genetics with new techniques in biophysics and structural biology. Our recent successes include the solution of the first crystal structure of a phage head-tail connector (gp10; Simpson et al. 2000) and scaffold protein (gp7; Morais et al. in preparation). These structures permit us to describe new models for the mechanism of DNA translocation during packaging and the nature of the scaffold core involved in prolate head shell assembly, respectively. We have put forward the testable hypothesis that the phi29 connector acts as a compressive ratchet, driving the DNA into the prohead shell while passively rotating to maintain register with the DNA helix. Phi29 has been used for the first time to demonstrate the dynamics of the DNA packaging process by the use of laser tweezers measurement of both the rate and the force of a single DNA packaging event (Smith et al. 2001). The phi29 DNA packaging machine is powerful, generating forces in the order of 60 picoNewtons. Ongoing single molecule efforts hope to reveal details of the biochemical events of DNA translocation by elucidating the sequence of steps as they relate to the biochemistry of ATP hydrolysis by the motor. Phi29 stands at the threshold of revealing the mechanism of DNA packaging and providing a launching point for understanding complex packaging events common to many viral systems. Simpson, A. A. et al. Nature 408, 745-750 (2000) Smith, D. E. et al. Nature 413, 748-752 (2001)