New techniques allow scientists to have direct observations of how DNA and genetic material is copied and repaired.

"We can monitor the process directly, and that gives us a different perspective," said Roberto Galletto, a postdoctoral scholar at UC Davis.

Scientists studied these processes in Escherichia coli bacteria. They found that an enzyme named RecA plays a vital role.

Molecules of the enzyme attach themselves along a DNA strand (molecule), stretching it out ( DNA molecules are normally tight curled) and forming a straight filament.

A complementary DNA molecule lines up along side it, and pieces of DNA can be changed in order to repair errors or gaps in the original strand.

In humans, the similar enzyme is named Rad51.

"How RecA and Rad51 assemble into filaments determines the outcome of DNA repair, but very little is known about how assembly is controlled," said Stephen Kowalczykowski, professor in the sections of Microbiology and of Molecular and Cellular Biology and director of the Center for Genetics and Development at UC Davis.

Genes implied in producing Rad51 enzyme have been linked to increased risk of breast cancer.

Galletto attached a short piece of DNA to a tiny latex bead and placed it in a flow chamber, held by laser beam "tweezers." Fluid flowing past made the DNA stream out like a banner.

DNA was in contact through an adjacent channel with fluorescently-tagged RecA.

He watched for the results on the first chamber after short periods of time.

Repeated introductions of the same piece of DNA into the fluorescent channel allowed the team to see the RecA enzyme formed clusters of four to five molecules on the DNA.

The formation of these clusters provoked a rapidly growth of the DNA/RecA filament in both directions.

"The measurements made in those experiments will be the baseline for future studies of both RecA and Rad51," Kowalczykowski said.

This study completes a previous work of Kowalczykowski and Ronald J. Baskin, professor of molecular and cellular biology, to study single enzymes at work stretching DNA molecules.