t a resolution of 35 angstroms, the 3-D images identify critical components of these "transcriptional factor" or TF proteins, including 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 production of proteins—or protein synthesis—begins when the electronic bonds that zip up dna�s double helix are undone and the two spiraling strands of bases are unwound. This leaves the genetic code contained on each strand of dna exposed and ready to be transcribed.