05-28-02, 02:11 PM
WEST LAFAYETTE, Ind. -- Long known as messengers, transcribers and translators for DNA, the hard-working family of RNA molecules may also serve as chauffeurs.
Peixuan Guo, professor of molecular virology at Purdue University, has found that a virus known as Bacteriophage Phi 29 uses six RNAs strung together in the shape of a hexagon to create a motor that transports DNA in the virus.
Read on... (http://news.uns.purdue.edu/UNS/html4ever/9808.Guo.RNA.html)
06-07-02, 08:59 PM
Dr. Carlos Bustamante gave a lexture at my school this week. He does single molecule measurements in phi29 packaging. The RNA seems to play a structural role (the reference you gave was 4 years old which is a long time in biology at the pace it's currently moving). The difference in the 5 fold and 6 fold structural elements in the colllar region of the motor is supposed to help encourage rotation, by not allowing a stable positioning of the two.
It's really cool though. The phage packages the DNA to 600mPa (a champagne bottle is about 6mPa). In this way it stores potential energy that helps drive the initial penetration of the DNA genome into the cell it's invading. Presumably the rest of the entry is actually driven by transcription (RNA polymerase as a motor can pull with forces of roughly 15-20 pico newtons, the packaging motor of the phage gets up to 55 pico newtons, myosin in muscle ~ 5-10 pico newtons) and entropic effects.
Anyway, I probably wouldn't do it justice in description. His group uses optical tweezers to measure the forces in single motors packaging phages (molecular motors operate near the thermal noise so they basically make mistakes, slip, etc a lot so to really understand the measurements you need to take a statistical approach). But I recommend reading some of his work if you can. His most recent is:
The bacteriophage [phi] 29 portal motor can package DNA against a large internal force
DOUGLAS E. SMITH, SANDER J. TANS, STEVEN B. SMITH, SHELLEY GRIMES§, DWIGHT L. ANDERSON & CARLOS BUSTAMANTE