Averell L. Gnatt 2026-11-05
Averell L. Gnatt studied the protein structure of RNA polymerase II, the enzyme that carries out much of eukaryotic transcription. In 2001, he and colleagues determined an X-ray crystallography structure of an actively transcribing complex at a spatial detail of . The complex contained both the DNA template and the growing RNA, allowing their paths through the enzyme to be followed.[ref]
Incoming paired DNA entered a cleft and separated before the active site. A nine-base-pair DNA-RNA hybrid held the newly copied region, while the growing RNA end lay at the site where the next nucleotide would be added. Thus only a short local stretch of the product remained paired to its template: the rest of the RNA could leave as copying continued. Comparison with the free enzyme also showed closure of a protein clamp over the bound DNA and RNA, connecting a change in protein structure with stable engagement during transcription.[ref]
Structural Basis of Transcription: An RNA Polymerase II Elongation Complex at 3.3 Å Resolution by Averell L. Gnatt and others. Abstract; nine-base-pair hybrid, RNA exit groove and clamp closure
Transcription elongation complex 2026-11-05
A transcription elongation complex is the working assembly of RNA polymerase, its DNA template and the growing RNA during transcript extension. The RNA end is positioned for addition of the next nucleotide; a short DNA-RNA hybrid helps organize the nucleic acids inside the enzyme. Additional proteins can associate with this core assembly.
A 2001 RNA polymerase II crystal structure at resolution showed entering duplex DNA, unwinding before the active site, and a nine-base pair DNA-RNA hybrid. Compared with free RNA polymerase II, the protein clamp closed around the nucleic acids. These observations connected a structurally identifiable assembly with ongoing transcription.[ref]
Structural Basis of Transcription: An RNA Polymerase II Elongation Complex at 3.3 Å Resolution by Averell L. Gnatt and others. Abstract: duplex entry, hybrid, RNA end and clamp changes
For a sequence example, a template segment read -TAC- specifies the complementary RNA segment -AUG-. Each addition extends the RNA while the complex advances relative to the template. This illustrates information flow; the three-letter example does not specify the complete set of contacts that stabilizes a real transcription elongation complex.