Presentation: Helicase

Speaker: Stephen Kowalczykowski, professor, Section of Microbiology and director, Center for Genes and Development

Symposium name: Nanotechnology 2003: Big Things in Little Packages

Symposium date and time: 2 p.m. to 5:40 p.m., Friday, Feb. 14.

Technology developed at the University of California, Davis, is allowing researchers to observe, for the first time, how a sequence of DNA can act as a "molecular throttle" to change the activity of an enzyme.

The researchers, led by Stephen Kowalczykowski, professor of microbiology and director of the UC Davis Center for Genes and Development, previously developed the method to film single molecules of the enzyme recBCD helicase at work unwinding a DNA double helix.

By exposing single strands of DNA, helicase activity is an essential first step in most processes involving DNA.

The researchers have now put recBCD onto DNA strands carrying the "chi" sequence, which is known to affect how efficiently genes following the sequence are read.

Using the single molecule apparatus, they found that when the recBCD molecule reaches the chi sequence, it stops for up to 10 seconds, then continues but at a slower rate.

"It's a complete surprise," Kowalczykowski said. The results would have been impossible to find with a conventional bulk experiment averaging the activity of many enzymes and DNA strands, he said.

Kowalczykowski believes that the change in velocity is due to one of two helicase subunits in recBCD being switched off by the chi sequence -- as if one motor had been shut off.

Kowalczykowski will illustrate the findings with real time movies during his presentation.