Structural biology: Pivotal findings for a transcription machine

Abstract

Crystal structures of the complete RNA Polymerase I complex are now revealed. These structures link opening and closing of the DNA binding cleft of this enzyme to control of transcription.

Figure 1. RNA Polymerase I (Pol I)

Front view of the 14-subunit Pol I complex with approximate locations of the core (blue) and shelf (red) modules, which broadly overlap the cleft sides formed by subunits A135 and A190, respectively, as well as the DNA-binding cleft. The open and closed states of the cleft are determined by relative pivoting of the core and shelf modules at the cleft base near the active site (arrows). Also indicated are: the permanently closed clamp; the fixed stalk, comprised of the A43-A14 sub-complex, which contributes to the permanent closure of the clamp; the active site of the enzyme, where RNA synthesis occurs; the TFIIS-like carboxy-terminal domain of A12.2, integral to the active site; and, the TFIIF-like A49-A34.5 sub-complex, which stabilizes A12.2.