July 2009 research highlight

Research highlights

PSI-SGKB [doi:10.1038/nsmb0709-683]

Ancient polymerase

The archaeal RNA polymerase shares structural similarities with eukaryotic RNA polymerase II, but differs in that the archaeal polymerase requires only two accessory factors whereas the eukaryotic version requires several. The overall structure of the archaeal RNA polymerase was recently described, but some of the subunits were missing. Now, Abrescia and colleagues complete the picture with the crystal structure of the 13-subunit RNA polymerase from Sulfolobus shibatae at 3.35 Å. The complete structure reveals two new subunits: Rpo8, which is equivalent to the eukaryotic Rbp8, and Rpo13, which has no ortholog in the eukaryotic complex. Both of these subunits were absent from the earlier archaeal polymerase structures. Although the function of Rpo13 is still unknown, its location suggests that it has a role in initiation and elongation. The authors indicate that Rpo13 could assist formation of the transcription bubble once the pre-initiation complex is formed. The structure of the RNA polymerase allied with modeling of the atomic details of Rpo13 suggest that its C terminus is about 7 Å from the phosphate group of the nucleotide at a position 8 residues downstream from the start site of the modeled nontemplate DNA strand. The authors suggest that Rpo13 acts as a 'lock point' against which the main body of the polymerase cleft can push or twist DNA. This could explain how Rpo13 performs some of the roles attributed to eukaryote-specific general transcription factors. (PLoS Biol. 7, e1000102, 2009)

Written by Maria Hodges