Localization of the yeast RNA polymerase I-specific subunits.
The spatial distribution of four subunits specifically associated to the yeast DNA-dependent RNA polymerase I (RNA pol I) was studied by electron microscopy. A structural model of the native enzyme was determined by cryo-electron microscopy from isolated molecules and was compared with the atomic structure of RNA pol II Delta 4/7, which lacks the specific polypeptides. The two models were aligned and a difference map revealed four additional protein densities present in RNA pol I, which were characterized by immunolabelling. A protruding protein density named stalk was found to contain the RNA pol I-specific subunits A43 and A14. The docking with the atomic structure showed that the stalk protruded from the structure at the same site as the C-terminal domain (CTD) of the largest subunit of RNA pol II. Subunit A49 was placed on top of the clamp whereas subunit A34.5 bound at the entrance of the DNA binding cleft, where it could contact the downstream DNA. The location of the RNA pol I-specific subunits is correlated with their biological activity.
Bischler
Nicolas
N
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, 1 rue Laurent Fries, BP163, F-67404 Illkirch Cedex, France.
Brino
Laurent
L
Carles
Christophe
C
Riva
Michel
M
Tschochner
Herbert
H
Mallouh
Véronique
V
Schultz
Patrick
P
D020285:Cryoelectron Microscopy; D007091:Image Processing, Computer-Assisted; D008958:Models, Molecular; D016624:Negative Staining; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D021122:Protein Subunits; D012318:RNA Polymerase I / Q000032:analysis* / Q000648:ultrastructure; D012319:RNA Polymerase II / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis* / Q000648:ultrastructure; D017384:Sequence Deletion
D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; D012318:RNA Polymerase I