Rewinding Motors

More on the nanomachinery that governs DNA processing.
Biologists Discover Motor Protein That Rewinds DNA

Quote:

ScienceDaily (Nov. 2, 2008) — Two biologists at the University of California, San Diego have discovered the first of a new class of cellular motor proteins that “rewind” sections of the double-stranded DNA molecule that become unwound, like the tangled ribbons from a cassette tape, in “bubbles” that prevent critical genes from being expressed.

Quote:

“When your DNA gets stuck in the unwound position, your cells are in big trouble, and in humans, that ultimately leads to death” said Jim Kadonaga, a professor of biology at UCSD who headed the study. “What we discovered is the enzyme that fixes this problem.” The discovery represents the first time scientists have identified a motor protein specifically designed to prevent the accumulation of bubbles of unwound DNA, which occurs when DNA strands become improperly unwound in certain locations along the molecule.

Quote:

“We knew this particular protein caused this disease before we started the study,” said Kadonaga. “That’s why we investigated it. We just didn’t know what it did.” What this protein, called HARP for HepA-related protein, did astounded Kadonaga and Timur Yusufzai, a postdoctoral fellow working in his laboratory. The two molecular biologists initially discovered that this motor protein burns energy in the same way as enzymes called helicases and, like helicases, attached to the dividing sections of DNA. But while helicases use their energy to separate two annealed nucleic acid strands—such as two strands of DNA, two strands of RNA or the strands of a RNA-DNA hybrid— the scientists found to their surprise that this protein did the opposite; that is, it rewinds sections of defective DNA and thus seals the two strands together again. As a consequence, the UCSD biologists termed their new enzyme activity an “annealing helicase.” “We didn’t even consider the idea of annealing helicases before this study started,” said Kadonaga. “It didn’t occur to us that such enzymes even existed. In fact, we never knew until now what happened to DNA when it got stuck in the unwound position.”

Clocks, motors, nanomachines etc. Superbly intelligent biomolecular machinery making life possible.