Structural biology of RNA polymerase III: subcomplex C17/25 X-ray structure and 11 subunit enzyme model

Mol Cell. 2006 Jul 7;23(1):71-81. doi: 10.1016/j.molcel.2006.05.013.


We obtained an 11 subunit model of RNA polymerase (Pol) III by combining a homology model of the nine subunit core enzyme with a new X-ray structure of the subcomplex C17/25. Compared to Pol II, Pol III shows a conserved active center for RNA synthesis but a structurally different upstream face for specific initiation complex assembly during promoter selection. The Pol III upstream face includes a HRDC domain in subunit C17 that is translated by 35 A and rotated by 150 degrees compared to its Pol II counterpart. The HRDC domain is essential in vivo, folds independently in vitro, and, unlike other HRDC domains, shows no indication of nucleic acid binding. Thus, the HRDC domain is a functional module that could account for the role of C17 in Pol III promoter-specific initiation. During elongation, C17/25 may bind Pol III transcripts emerging from the adjacent exit pore, because the subcomplex binds to tRNA in vitro.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Crystallography, X-Ray
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Subunits / chemistry
  • Protein Subunits / genetics
  • Protein Subunits / physiology
  • RNA Polymerase II / chemistry
  • RNA Polymerase II / genetics
  • RNA Polymerase II / physiology
  • RNA Polymerase III / chemistry*
  • RNA Polymerase III / genetics
  • RNA Polymerase III / physiology
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / physiology
  • Sequence Alignment


  • Protein Subunits
  • Saccharomyces cerevisiae Proteins
  • C17 protein, S cerevisiae
  • C25 protein, S cerevisiae
  • RNA Polymerase II
  • RNA Polymerase III

Associated data

  • PDB/2CKZ