Tuesday, September 29, 2009

Polymerase: Taking 30 steps forward, taking two steps back ...

The body's nanomachines that read our genes don't run as smoothly as previously thought, according to a new study by University of California, Berkeley, scientists. When these nanoscale protein machines encounter obstacles as they move along the DNA, they stall, often for minutes, and even backtrack as they transcribe DNA that is tightly wound to fit inside the cell's nucleus.

For over 30 years, scientists had wondered how the polymerase responded to the nucleosome, and we were finally able to observe this process directly," Hodges said. "People thought that the polymerase is a powerful motor that would blow through the nucleosome like a bulldozer, but it's surprisingly delicate in its response; if anything is in the way, Pol II stops and backs up.

RNA polymerase II performing gene expression
RNA polymerase II (blue) performs the first step of gene expression by moving along the cell's DNA (gray) and transcribing it into messenger RNA (red). During this process, the polymerase encounters obstacles, such as nucleosomes, which tightly wrap the DNA around histone proteins (yellow) and prevent continued transcription. UC Berkeley researchers have developed methods to directly observe this process in real time. (Courtney Hodges/UC Berkeley)