These research findings of Rockefeller University scientists illuminate how the process of transcription begins in bacteria. Understanding this process may provide clues for developing new drugs to treat bacterial infections.
The DNA-transcribing machinery is called the RNA polymerase (RNAP). The RNAP comprises a core enzyme, which can synthesize RNA from a DNA template, but cannot initiate transcription by itself. Initiation requires another protein, the sigma subunit, which binds core to form the holoenzyme.
The sigma subunit "tells" RNAP where in the genomic DNA to start transcription. It does this by recognizing a section of the genes DNA called the promoter region and "melting" the DNA to expose one of the double-helical strands the RNAP will use as the template to synthesize RNA.
The Rockefeller researchers, led by Seth Darst, Ph.D., studied RNAP from a bacterium called Thermus aquaticus, a member of a family of organisms that thrive at high temperatures. They used a technique called X-ray crystallography to reveal the structure of the holoenzyme, the core enzyme bound to the sigma subunit. They also used this research tool to visualize the structure of the holoenzyme bound to a short piece of DNA containing a promoter sequence.
In X-ray crystallography, X-rays are fired at crystallized proteins or complexes of proteins bound to other molecules. Analysis of the data from the diffracted X-rays yields information about the three-dimensional structure of the molecule. Some molecules can be visualized at the resolution of a few angstroms (a typical atom is roughly two angstroms in diameter). But Darst notes that the crystals his group used did not diffra
Contact: Joseph Bonner