Electron crystal structure of an RNA polymerase II transcription elongation complex

The structure of an actively transcribing complex, containing yeast RNA pol ymerase II with associated template DNA and product RNA, was determined by electron crystallography. Nucleic acid, in all likelihood the "transcriptio n bubble" at the active center of the enzyme, occupies a previously noted 2 5 Angstrom channel in the protein structure. Details are indicative of a ro ughly 90 degrees bend of the DNA between upstream and downstream regions. T he DNA apparently lies entirely on one face of the polymerase, rather than passing through a hole to the opposite side, as previously suggested.