BERKELEY, CA -- A combination of electron microscopy and single particle image analysis has been used to produce the first three-dimensional images of the protein complex that initiates the transcription of DNA's genetic code for the subsequent production of new proteins. The research was conducted by scientists with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley. The 3-D images, at a resolution of 35 angstroms (atoms typically have a radius of one to two angstroms), identify critical components of a complex of transcriptional factor (TF) proteins that include TFIID, TFIIA and TFIIB. A model reconstructed from the images shows TFIID as a horseshoe-shaped structure surrounding a central cavity inside of which recognition and binding to DNA takes place. TFIIA and TFIIB are shown to bind to the TFIID in a way that affects the size and shape of the cavity.
The research team that produced these images was led by Eva Nogales who holds a joint appointment with Berkeley Lab's Life Sciences Division and UC Berkeley's Molecular and Cell Biology Department. Other team members were Frank Andel, of Berkeley Lab, and Andreas Ladurner, Carla Inouye, and Robert Tjian of UC Berkeley. Tjian is also affiliated with the Howard Hughes Medical Institute. Their results were published in the December 10, 1999 issue of the journal Science.
After a strand of DNA has been unwound and unzipped in preparation for protein production, TFIID binds to an exposed DNA section precisely where a genetic message begins. Once TFIID recognizes and binds to a gene on a strand of DNA, it interacts with RNA polymerase so that the genetic code is transcribed into messenger RNA which then carries the information out of the cell's nucleus and into its cytoplasm where proteins are assembled.
"Our 3-D reconstruction gives us a good idea as to how TFIID works in concert with TFIIA and TFIIB to initiate and regul
Contact: Lynn Yarris
DOE/Lawrence Berkeley National Laboratory