To see an RNA polymerase II (Pol II) in action has been the dream of any molecular biologist. Imaging the possibilities to see and not to suspect transcription of DNA into RNA, to see what the interactions are and not to suppose. A team around Guillermo Calero in Pittsburgh, PA, and Craig D. Kaplan at Texas, A & M University, has achieved this molecular dream.

The paper in Molecular Cell by C.O. Barnes and M. Calero depicts the crystal structure of a RNA Pol II complex together with DNA and the newly transcribed RNA stabilized by transcription factor II F (TFIIF). The structure from Saccharomyces cerevisiae reveals  the unwinding of the the DNA duplex, the so-called nucleic acid scaffold (NAS) where the RNA is formed and the downstream duplex. The down stream duplex builds a 130 ° degree angle to the upstream duplex in the complex.  The pictures show for the first time the unwinding of DNA, the RNA synthesis, the re-winding, and the contributions of the different Pol II subunits.

Unfortunately the accession numbers for the structure are not yet availabe in the Protein Data Bank (5C4X/A/4/J, 5C3E). (They are now.)

This paper is a must for any one teaching molecular biology, for students in any case.